os
— Miscellaneous operating system interfaces¶
Source code: Lib/os.py
This module provides a portable way of using operating system dependent
functionality. If you just want to read or write a file see open()
, if
you want to manipulate paths, see the os.path
module, and if you want to
read all the lines in all the files on the command line see the fileinput
module. For creating temporary files and directories see the tempfile
module, and for high-level file and directory handling see the shutil
module.
Notes on the availability of these functions:
The design of all built-in operating system dependent modules of Python is such that as long as the same functionality is available, it uses the same interface; for example, the function
os.stat(path)
returns stat information about path in the same format (which happens to have originated with the POSIX interface).Extensions peculiar to a particular operating system are also available through the
os
module, but using them is of course a threat to portability.All functions accepting path or file names accept both bytes and string objects, and result in an object of the same type, if a path or file name is returned.
On VxWorks, os.popen, os.fork, os.execv and os.spawn*p* are not supported.
On WebAssembly platforms, Android and iOS, large parts of the
os
module are not available or behave differently. APIs related to processes (e.g.fork()
,execve()
) and resources (e.g.nice()
) are not available. Others likegetuid()
andgetpid()
are emulated or stubs. WebAssembly platforms also lack support for signals (e.g.kill()
,wait()
).
Note
All functions in this module raise OSError
(or subclasses thereof) in
the case of invalid or inaccessible file names and paths, or other arguments
that have the correct type, but are not accepted by the operating system.
- os.name¶
The name of the operating system dependent module imported. The following names have currently been registered:
'posix'
,'nt'
,'java'
.See also
sys.platform
has a finer granularity.os.uname()
gives system-dependent version information.The
platform
module provides detailed checks for the system’s identity.
File Names, Command Line Arguments, and Environment Variables¶
In Python, file names, command line arguments, and environment variables are
represented using the string type. On some systems, decoding these strings to
and from bytes is necessary before passing them to the operating system. Python
uses the filesystem encoding and error handler to perform this
conversion (see sys.getfilesystemencoding()
).
The filesystem encoding and error handler are configured at Python
startup by the PyConfig_Read()
function: see
filesystem_encoding
and
filesystem_errors
members of PyConfig
.
Changed in version 3.1: On some systems, conversion using the file system encoding may fail. In this case, Python uses the surrogateescape encoding error handler, which means that undecodable bytes are replaced by a Unicode character U+DCxx on decoding, and these are again translated to the original byte on encoding.
The file system encoding must
guarantee to successfully decode all bytes below 128. If the file system
encoding fails to provide this guarantee, API functions can raise
UnicodeError
.
See also the locale encoding.
Python UTF-8 Mode¶
Added in version 3.7: See PEP 540 for more details.
The Python UTF-8 Mode ignores the locale encoding and forces the usage of the UTF-8 encoding:
Use UTF-8 as the filesystem encoding.
sys.getfilesystemencoding()
returns'utf-8'
.locale.getpreferredencoding()
returns'utf-8'
(the do_setlocale argument has no effect).sys.stdin
,sys.stdout
, andsys.stderr
all use UTF-8 as their text encoding, with thesurrogateescape
error handler being enabled forsys.stdin
andsys.stdout
(sys.stderr
continues to usebackslashreplace
as it does in the default locale-aware mode)On Unix,
os.device_encoding()
returns'utf-8'
rather than the device encoding.
Note that the standard stream settings in UTF-8 mode can be overridden by
PYTHONIOENCODING
(just as they can be in the default locale-aware
mode).
As a consequence of the changes in those lower level APIs, other higher level APIs also exhibit different default behaviours:
Command line arguments, environment variables and filenames are decoded to text using the UTF-8 encoding.
os.fsdecode()
andos.fsencode()
use the UTF-8 encoding.open()
,io.open()
, andcodecs.open()
use the UTF-8 encoding by default. However, they still use the strict error handler by default so that attempting to open a binary file in text mode is likely to raise an exception rather than producing nonsense data.
The Python UTF-8 Mode is enabled if the LC_CTYPE locale is
C
or POSIX
at Python startup (see the PyConfig_Read()
function).
It can be enabled or disabled using the -X utf8
command line
option and the PYTHONUTF8
environment variable.
If the PYTHONUTF8
environment variable is not set at all, then the
interpreter defaults to using the current locale settings, unless the current
locale is identified as a legacy ASCII-based locale (as described for
PYTHONCOERCECLOCALE
), and locale coercion is either disabled or
fails. In such legacy locales, the interpreter will default to enabling UTF-8
mode unless explicitly instructed not to do so.
The Python UTF-8 Mode can only be enabled at the Python startup. Its value
can be read from sys.flags.utf8_mode
.
See also the UTF-8 mode on Windows and the filesystem encoding and error handler.
See also
- PEP 686
Python 3.15 will make Python UTF-8 Mode default.
Process Parameters¶
These functions and data items provide information and operate on the current process and user.
- os.ctermid()¶
Return the filename corresponding to the controlling terminal of the process.
Availability: Unix, not WASI.
- os.environ¶
A mapping object where keys and values are strings that represent the process environment. For example,
environ['HOME']
is the pathname of your home directory (on some platforms), and is equivalent togetenv("HOME")
in C.This mapping is captured the first time the
os
module is imported, typically during Python startup as part of processingsite.py
. Changes to the environment made after this time are not reflected inos.environ
, except for changes made by modifyingos.environ
directly.The
os.environ.refresh()
method updatesos.environ
with changes to the environment made byos.putenv()
, byos.unsetenv()
, or made outside Python in the same process.This mapping may be used to modify the environment as well as query the environment.
putenv()
will be called automatically when the mapping is modified.On Unix, keys and values use
sys.getfilesystemencoding()
and'surrogateescape'
error handler. Useenvironb
if you would like to use a different encoding.On Windows, the keys are converted to uppercase. This also applies when getting, setting, or deleting an item. For example,
environ['monty'] = 'python'
maps the key'MONTY'
to the value'python'
.Note
Calling
putenv()
directly does not changeos.environ
, so it’s better to modifyos.environ
.Note
On some platforms, including FreeBSD and macOS, setting
environ
may cause memory leaks. Refer to the system documentation forputenv()
.You can delete items in this mapping to unset environment variables.
unsetenv()
will be called automatically when an item is deleted fromos.environ
, and when one of thepop()
orclear()
methods is called.Changed in version 3.9: Updated to support PEP 584’s merge (
|
) and update (|=
) operators.Changed in version 3.14: Added the
os.environ.refresh()
method.
- os.environb¶
Bytes version of
environ
: a mapping object where both keys and values arebytes
objects representing the process environment.environ
andenvironb
are synchronized (modifyingenvironb
updatesenviron
, and vice versa).environb
is only available ifsupports_bytes_environ
isTrue
.Added in version 3.2.
Changed in version 3.9: Updated to support PEP 584’s merge (
|
) and update (|=
) operators.
- os.chdir(path)
- os.fchdir(fd)
- os.getcwd()
These functions are described in Files and Directories.
- os.fsencode(filename)¶
Encode path-like filename to the filesystem encoding and error handler; return
bytes
unchanged.fsdecode()
is the reverse function.Added in version 3.2.
Changed in version 3.6: Support added to accept objects implementing the
os.PathLike
interface.
- os.fsdecode(filename)¶
Decode the path-like filename from the filesystem encoding and error handler; return
str
unchanged.fsencode()
is the reverse function.Added in version 3.2.
Changed in version 3.6: Support added to accept objects implementing the
os.PathLike
interface.
- os.fspath(path)¶
Return the file system representation of the path.
If
str
orbytes
is passed in, it is returned unchanged. Otherwise__fspath__()
is called and its value is returned as long as it is astr
orbytes
object. In all other cases,TypeError
is raised.Added in version 3.6.
- class os.PathLike¶
An abstract base class for objects representing a file system path, e.g.
pathlib.PurePath
.Added in version 3.6.
- os.getenv(key, default=None)¶
Return the value of the environment variable key as a string if it exists, or default if it doesn’t. key is a string. Note that since
getenv()
usesos.environ
, the mapping ofgetenv()
is similarly also captured on import, and the function may not reflect future environment changes.On Unix, keys and values are decoded with
sys.getfilesystemencoding()
and'surrogateescape'
error handler. Useos.getenvb()
if you would like to use a different encoding.Availability: Unix, Windows.
- os.getenvb(key, default=None)¶
Return the value of the environment variable key as bytes if it exists, or default if it doesn’t. key must be bytes. Note that since
getenvb()
usesos.environb
, the mapping ofgetenvb()
is similarly also captured on import, and the function may not reflect future environment changes.getenvb()
is only available ifsupports_bytes_environ
isTrue
.Availability: Unix.
Added in version 3.2.
- os.get_exec_path(env=None)¶
Returns the list of directories that will be searched for a named executable, similar to a shell, when launching a process. env, when specified, should be an environment variable dictionary to lookup the PATH in. By default, when env is
None
,environ
is used.Added in version 3.2.
- os.getegid()¶
Return the effective group id of the current process. This corresponds to the “set id” bit on the file being executed in the current process.
Availability: Unix, not WASI.
- os.geteuid()¶
Return the current process’s effective user id.
Availability: Unix, not WASI.
- os.getgid()¶
Return the real group id of the current process.
Availability: Unix.
The function is a stub on WASI, see WebAssembly platforms for more information.
- os.getgrouplist(user, group, /)¶
Return list of group ids that user belongs to. If group is not in the list, it is included; typically, group is specified as the group ID field from the password record for user, because that group ID will otherwise be potentially omitted.
Availability: Unix, not WASI.
Added in version 3.3.
- os.getgroups()¶
Return list of supplemental group ids associated with the current process.
Availability: Unix, not WASI.
Note
On macOS,
getgroups()
behavior differs somewhat from other Unix platforms. If the Python interpreter was built with a deployment target of10.5
or earlier,getgroups()
returns the list of effective group ids associated with the current user process; this list is limited to a system-defined number of entries, typically 16, and may be modified by calls tosetgroups()
if suitably privileged. If built with a deployment target greater than10.5
,getgroups()
returns the current group access list for the user associated with the effective user id of the process; the group access list may change over the lifetime of the process, it is not affected by calls tosetgroups()
, and its length is not limited to 16. The deployment target value,MACOSX_DEPLOYMENT_TARGET
, can be obtained withsysconfig.get_config_var()
.
- os.getlogin()¶
Return the name of the user logged in on the controlling terminal of the process. For most purposes, it is more useful to use
getpass.getuser()
since the latter checks the environment variablesLOGNAME
orUSERNAME
to find out who the user is, and falls back topwd.getpwuid(os.getuid())[0]
to get the login name of the current real user id.Availability: Unix, Windows, not WASI.
- os.getpgid(pid)¶
Return the process group id of the process with process id pid. If pid is 0, the process group id of the current process is returned.
Availability: Unix, not WASI.
- os.getpgrp()¶
Return the id of the current process group.
Availability: Unix, not WASI.
- os.getpid()¶
Return the current process id.
The function is a stub on WASI, see WebAssembly platforms for more information.
- os.getppid()¶
Return the parent’s process id. When the parent process has exited, on Unix the id returned is the one of the init process (1), on Windows it is still the same id, which may be already reused by another process.
Availability: Unix, Windows, not WASI.
Changed in version 3.2: Added support for Windows.
- os.getpriority(which, who)¶
Get program scheduling priority. The value which is one of
PRIO_PROCESS
,PRIO_PGRP
, orPRIO_USER
, and who is interpreted relative to which (a process identifier forPRIO_PROCESS
, process group identifier forPRIO_PGRP
, and a user ID forPRIO_USER
). A zero value for who denotes (respectively) the calling process, the process group of the calling process, or the real user ID of the calling process.Availability: Unix, not WASI.
Added in version 3.3.
- os.PRIO_PROCESS¶
- os.PRIO_PGRP¶
- os.PRIO_USER¶
Parameters for the
getpriority()
andsetpriority()
functions.Availability: Unix, not WASI.
Added in version 3.3.
- os.PRIO_DARWIN_THREAD¶
- os.PRIO_DARWIN_PROCESS¶
- os.PRIO_DARWIN_BG¶
- os.PRIO_DARWIN_NONUI¶
Parameters for the
getpriority()
andsetpriority()
functions.Availability: macOS
Added in version 3.12.
- os.getresuid()¶
Return a tuple (ruid, euid, suid) denoting the current process’s real, effective, and saved user ids.
Availability: Unix, not WASI.
Added in version 3.2.
- os.getresgid()¶
Return a tuple (rgid, egid, sgid) denoting the current process’s real, effective, and saved group ids.
Availability: Unix, not WASI.
Added in version 3.2.
- os.getuid()¶
Return the current process’s real user id.
Availability: Unix.
The function is a stub on WASI, see WebAssembly platforms for more information.
- os.initgroups(username, gid, /)¶
Call the system initgroups() to initialize the group access list with all of the groups of which the specified username is a member, plus the specified group id.
Availability: Unix, not WASI, not Android.
Added in version 3.2.
- os.putenv(key, value, /)¶
Set the environment variable named key to the string value. Such changes to the environment affect subprocesses started with
os.system()
,popen()
orfork()
andexecv()
.Assignments to items in
os.environ
are automatically translated into corresponding calls toputenv()
; however, calls toputenv()
don’t updateos.environ
, so it is actually preferable to assign to items ofos.environ
. This also applies togetenv()
andgetenvb()
, which respectively useos.environ
andos.environb
in their implementations.See also the
os.environ.refresh()
method.Note
On some platforms, including FreeBSD and macOS, setting
environ
may cause memory leaks. Refer to the system documentation forputenv()
.Raises an auditing event
os.putenv
with argumentskey
,value
.Changed in version 3.9: The function is now always available.
- os.setegid(egid, /)¶
Set the current process’s effective group id.
Availability: Unix, not WASI, not Android.
- os.seteuid(euid, /)¶
Set the current process’s effective user id.
Availability: Unix, not WASI, not Android.
- os.setgid(gid, /)¶
Set the current process’ group id.
Availability: Unix, not WASI, not Android.
- os.setgroups(groups, /)¶
Set the list of supplemental group ids associated with the current process to groups. groups must be a sequence, and each element must be an integer identifying a group. This operation is typically available only to the superuser.
Availability: Unix, not WASI.
Note
On macOS, the length of groups may not exceed the system-defined maximum number of effective group ids, typically 16. See the documentation for
getgroups()
for cases where it may not return the same group list set by calling setgroups().
- os.setns(fd, nstype=0)¶
Reassociate the current thread with a Linux namespace. See the setns(2) and namespaces(7) man pages for more details.
If fd refers to a
/proc/pid/ns/
link,setns()
reassociates the calling thread with the namespace associated with that link, and nstype may be set to one of the CLONE_NEW* constants to impose constraints on the operation (0
means no constraints).Since Linux 5.8, fd may refer to a PID file descriptor obtained from
pidfd_open()
. In this case,setns()
reassociates the calling thread into one or more of the same namespaces as the thread referred to by fd. This is subject to any constraints imposed by nstype, which is a bit mask combining one or more of the CLONE_NEW* constants, e.g.setns(fd, os.CLONE_NEWUTS | os.CLONE_NEWPID)
. The caller’s memberships in unspecified namespaces are left unchanged.fd can be any object with a
fileno()
method, or a raw file descriptor.This example reassociates the thread with the
init
process’s network namespace:fd = os.open("/proc/1/ns/net", os.O_RDONLY) os.setns(fd, os.CLONE_NEWNET) os.close(fd)
Availability: Linux >= 3.0 with glibc >= 2.14.
Added in version 3.12.
See also
The
unshare()
function.
- os.setpgrp()¶
Call the system call
setpgrp()
orsetpgrp(0, 0)
depending on which version is implemented (if any). See the Unix manual for the semantics.Availability: Unix, not WASI.
- os.setpgid(pid, pgrp, /)¶
Call the system call
setpgid()
to set the process group id of the process with id pid to the process group with id pgrp. See the Unix manual for the semantics.Availability: Unix, not WASI.
- os.setpriority(which, who, priority)¶
Set program scheduling priority. The value which is one of
PRIO_PROCESS
,PRIO_PGRP
, orPRIO_USER
, and who is interpreted relative to which (a process identifier forPRIO_PROCESS
, process group identifier forPRIO_PGRP
, and a user ID forPRIO_USER
). A zero value for who denotes (respectively) the calling process, the process group of the calling process, or the real user ID of the calling process. priority is a value in the range -20 to 19. The default priority is 0; lower priorities cause more favorable scheduling.Availability: Unix, not WASI.
Added in version 3.3.
- os.setregid(rgid, egid, /)¶
Set the current process’s real and effective group ids.
Availability: Unix, not WASI, not Android.
- os.setresgid(rgid, egid, sgid, /)¶
Set the current process’s real, effective, and saved group ids.
Availability: Unix, not WASI, not Android.
Added in version 3.2.
- os.setresuid(ruid, euid, suid, /)¶
Set the current process’s real, effective, and saved user ids.
Availability: Unix, not WASI, not Android.
Added in version 3.2.
- os.setreuid(ruid, euid, /)¶
Set the current process’s real and effective user ids.
Availability: Unix, not WASI, not Android.
- os.getsid(pid, /)¶
Call the system call
getsid()
. See the Unix manual for the semantics.Availability: Unix, not WASI.
- os.setsid()¶
Call the system call
setsid()
. See the Unix manual for the semantics.Availability: Unix, not WASI.
- os.setuid(uid, /)¶
Set the current process’s user id.
Availability: Unix, not WASI, not Android.
- os.strerror(code, /)¶
Return the error message corresponding to the error code in code. On platforms where
strerror()
returnsNULL
when given an unknown error number,ValueError
is raised.
- os.supports_bytes_environ¶
True
if the native OS type of the environment is bytes (eg.False
on Windows).Added in version 3.2.
- os.umask(mask, /)¶
Set the current numeric umask and return the previous umask.
The function is a stub on WASI, see WebAssembly platforms for more information.
- os.uname()¶
Returns information identifying the current operating system. The return value is an object with five attributes:
sysname
- operating system namenodename
- name of machine on network (implementation-defined)release
- operating system releaseversion
- operating system versionmachine
- hardware identifier
For backwards compatibility, this object is also iterable, behaving like a five-tuple containing
sysname
,nodename
,release
,version
, andmachine
in that order.Some systems truncate
nodename
to 8 characters or to the leading component; a better way to get the hostname issocket.gethostname()
or evensocket.gethostbyaddr(socket.gethostname())
.On macOS, iOS and Android, this returns the kernel name and version (i.e.,
'Darwin'
on macOS and iOS;'Linux'
on Android).platform.uname()
can be used to get the user-facing operating system name and version on iOS and Android.Availability: Unix.
Changed in version 3.3: Return type changed from a tuple to a tuple-like object with named attributes.
- os.unsetenv(key, /)¶
Unset (delete) the environment variable named key. Such changes to the environment affect subprocesses started with
os.system()
,popen()
orfork()
andexecv()
.Deletion of items in
os.environ
is automatically translated into a corresponding call tounsetenv()
; however, calls tounsetenv()
don’t updateos.environ
, so it is actually preferable to delete items ofos.environ
.See also the
os.environ.refresh()
method.Raises an auditing event
os.unsetenv
with argumentkey
.Changed in version 3.9: The function is now always available and is also available on Windows.
Disassociate parts of the process execution context, and move them into a newly created namespace. See the unshare(2) man page for more details. The flags argument is a bit mask, combining zero or more of the CLONE_* constants, that specifies which parts of the execution context should be unshared from their existing associations and moved to a new namespace. If the flags argument is
0
, no changes are made to the calling process’s execution context.Availability: Linux >= 2.6.16.
Added in version 3.12.
See also
The
setns()
function.
File Object Creation¶
These functions create new file objects. (See also
open()
for opening file descriptors.)
File Descriptor Operations¶
These functions operate on I/O streams referenced using file descriptors.
File descriptors are small integers corresponding to a file that has been opened by the current process. For example, standard input is usually file descriptor 0, standard output is 1, and standard error is 2. Further files opened by a process will then be assigned 3, 4, 5, and so forth. The name “file descriptor” is slightly deceptive; on Unix platforms, sockets and pipes are also referenced by file descriptors.
The fileno()
method can be used to obtain the file descriptor
associated with a file object when required. Note that using the file
descriptor directly will bypass the file object methods, ignoring aspects such
as internal buffering of data.
- os.close(fd)¶
Close file descriptor fd.
- os.closerange(fd_low, fd_high, /)¶
Close all file descriptors from fd_low (inclusive) to fd_high (exclusive), ignoring errors. Equivalent to (but much faster than):
for fd in range(fd_low, fd_high): try: os.close(fd) except OSError: pass
- os.copy_file_range(src, dst, count, offset_src=None, offset_dst=None)¶
Copy count bytes from file descriptor src, starting from offset offset_src, to file descriptor dst, starting from offset offset_dst. If offset_src is
None
, then src is read from the current position; respectively for offset_dst.In Linux kernel older than 5.3, the files pointed to by src and dst must reside in the same filesystem, otherwise an
OSError
is raised witherrno
set toerrno.EXDEV
.This copy is done without the additional cost of transferring data from the kernel to user space and then back into the kernel. Additionally, some filesystems could implement extra optimizations, such as the use of reflinks (i.e., two or more inodes that share pointers to the same copy-on-write disk blocks; supported file systems include btrfs and XFS) and server-side copy (in the case of NFS).
The function copies bytes between two file descriptors. Text options, like the encoding and the line ending, are ignored.
The return value is the amount of bytes copied. This could be less than the amount requested.
Note
On Linux,
os.copy_file_range()
should not be used for copying a range of a pseudo file from a special filesystem like procfs and sysfs. It will always copy no bytes and return 0 as if the file was empty because of a known Linux kernel issue.Availability: Linux >= 4.5 with glibc >= 2.27.
Added in version 3.8.
- os.device_encoding(fd)¶
Return a string describing the encoding of the device associated with fd if it is connected to a terminal; else return
None
.On Unix, if the Python UTF-8 Mode is enabled, return
'UTF-8'
rather than the device encoding.Changed in version 3.10: On Unix, the function now implements the Python UTF-8 Mode.
- os.dup(fd, /)¶
Return a duplicate of file descriptor fd. The new file descriptor is non-inheritable.
On Windows, when duplicating a standard stream (0: stdin, 1: stdout, 2: stderr), the new file descriptor is inheritable.
Availability: not WASI.
Changed in version 3.4: The new file descriptor is now non-inheritable.
- os.dup2(fd, fd2, inheritable=True)¶
Duplicate file descriptor fd to fd2, closing the latter first if necessary. Return fd2. The new file descriptor is inheritable by default or non-inheritable if inheritable is
False
.Availability: not WASI.
Changed in version 3.4: Add the optional inheritable parameter.
Changed in version 3.7: Return fd2 on success. Previously,
None
was always returned.
- os.fchmod(fd, mode)¶
Change the mode of the file given by fd to the numeric mode. See the docs for
chmod()
for possible values of mode. As of Python 3.3, this is equivalent toos.chmod(fd, mode)
.Raises an auditing event
os.chmod
with argumentspath
,mode
,dir_fd
.Availability: Unix, Windows.
The function is limited on WASI, see WebAssembly platforms for more information.
Changed in version 3.13: Added support on Windows.
- os.fchown(fd, uid, gid)¶
Change the owner and group id of the file given by fd to the numeric uid and gid. To leave one of the ids unchanged, set it to -1. See
chown()
. As of Python 3.3, this is equivalent toos.chown(fd, uid, gid)
.Raises an auditing event
os.chown
with argumentspath
,uid
,gid
,dir_fd
.Availability: Unix.
The function is limited on WASI, see WebAssembly platforms for more information.
- os.fdatasync(fd)¶
Force write of file with filedescriptor fd to disk. Does not force update of metadata.
Availability: Unix.
Note
This function is not available on MacOS.
- os.fpathconf(fd, name, /)¶
Return system configuration information relevant to an open file. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX.1, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given in the
pathconf_names
dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.If name is a string and is not known,
ValueError
is raised. If a specific value for name is not supported by the host system, even if it is included inpathconf_names
, anOSError
is raised witherrno.EINVAL
for the error number.As of Python 3.3, this is equivalent to
os.pathconf(fd, name)
.Availability: Unix.
- os.fstat(fd)¶
Get the status of the file descriptor fd. Return a
stat_result
object.As of Python 3.3, this is equivalent to
os.stat(fd)
.See also
The
stat()
function.
- os.fstatvfs(fd, /)¶
Return information about the filesystem containing the file associated with file descriptor fd, like
statvfs()
. As of Python 3.3, this is equivalent toos.statvfs(fd)
.Availability: Unix.
- os.fsync(fd)¶
Force write of file with filedescriptor fd to disk. On Unix, this calls the native
fsync()
function; on Windows, the MS_commit()
function.If you’re starting with a buffered Python file object f, first do
f.flush()
, and then doos.fsync(f.fileno())
, to ensure that all internal buffers associated with f are written to disk.Availability: Unix, Windows.
- os.ftruncate(fd, length, /)¶
Truncate the file corresponding to file descriptor fd, so that it is at most length bytes in size. As of Python 3.3, this is equivalent to
os.truncate(fd, length)
.Raises an auditing event
os.truncate
with argumentsfd
,length
.Availability: Unix, Windows.
Changed in version 3.5: Added support for Windows
- os.get_blocking(fd, /)¶
Get the blocking mode of the file descriptor:
False
if theO_NONBLOCK
flag is set,True
if the flag is cleared.See also
set_blocking()
andsocket.socket.setblocking()
.Availability: Unix, Windows.
The function is limited on WASI, see WebAssembly platforms for more information.
On Windows, this function is limited to pipes.
Added in version 3.5.
Changed in version 3.12: Added support for pipes on Windows.
- os.grantpt(fd, /)¶
Grant access to the slave pseudo-terminal device associated with the master pseudo-terminal device to which the file descriptor fd refers. The file descriptor fd is not closed upon failure.
Calls the C standard library function
grantpt()
.Availability: Unix, not WASI.
Added in version 3.13.
- os.isatty(fd, /)¶
Return
True
if the file descriptor fd is open and connected to a tty(-like) device, elseFalse
.
- os.lockf(fd, cmd, len, /)¶
Apply, test or remove a POSIX lock on an open file descriptor. fd is an open file descriptor. cmd specifies the command to use - one of
F_LOCK
,F_TLOCK
,F_ULOCK
orF_TEST
. len specifies the section of the file to lock.Raises an auditing event
os.lockf
with argumentsfd
,cmd
,len
.Availability: Unix.
Added in version 3.3.
- os.F_LOCK¶
- os.F_TLOCK¶
- os.F_ULOCK¶
- os.F_TEST¶
Flags that specify what action
lockf()
will take.Availability: Unix.
Added in version 3.3.
- os.login_tty(fd, /)¶
Prepare the tty of which fd is a file descriptor for a new login session. Make the calling process a session leader; make the tty the controlling tty, the stdin, the stdout, and the stderr of the calling process; close fd.
Availability: Unix, not WASI.
Added in version 3.11.
- os.lseek(fd, pos, whence, /)¶
Set the current position of file descriptor fd to position pos, modified by whence, and return the new position in bytes relative to the start of the file. Valid values for whence are:
SEEK_SET
or0
– set pos relative to the beginning of the fileSEEK_CUR
or1
– set pos relative to the current file positionSEEK_END
or2
– set pos relative to the end of the fileSEEK_HOLE
– set pos to the next data location, relative to posSEEK_DATA
– set pos to the next data hole, relative to pos
Changed in version 3.3: Add support for
SEEK_HOLE
andSEEK_DATA
.
- os.SEEK_SET¶
- os.SEEK_CUR¶
- os.SEEK_END¶
Parameters to the
lseek()
function and theseek()
method on file-like objects, for whence to adjust the file position indicator.SEEK_SET
Adjust the file position relative to the beginning of the file.
SEEK_CUR
Adjust the file position relative to the current file position.
SEEK_END
Adjust the file position relative to the end of the file.
Their values are 0, 1, and 2, respectively.
- os.SEEK_HOLE¶
- os.SEEK_DATA¶
Parameters to the
lseek()
function and theseek()
method on file-like objects, for seeking file data and holes on sparsely allocated files.SEEK_DATA
Adjust the file offset to the next location containing data, relative to the seek position.
SEEK_HOLE
Adjust the file offset to the next location containing a hole, relative to the seek position. A hole is defined as a sequence of zeros.
Note
These operations only make sense for filesystems that support them.
Availability: Linux >= 3.1, macOS, Unix
Added in version 3.3.
- os.open(path, flags, mode=0o777, *, dir_fd=None)¶
Open the file path and set various flags according to flags and possibly its mode according to mode. When computing mode, the current umask value is first masked out. Return the file descriptor for the newly opened file. The new file descriptor is non-inheritable.
For a description of the flag and mode values, see the C run-time documentation; flag constants (like
O_RDONLY
andO_WRONLY
) are defined in theos
module. In particular, on Windows addingO_BINARY
is needed to open files in binary mode.This function can support paths relative to directory descriptors with the dir_fd parameter.
Raises an auditing event
open
with argumentspath
,mode
,flags
.Changed in version 3.4: The new file descriptor is now non-inheritable.
Note
This function is intended for low-level I/O. For normal usage, use the built-in function
open()
, which returns a file object withread()
andwrite()
methods (and many more). To wrap a file descriptor in a file object, usefdopen()
.Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an
InterruptedError
exception (see PEP 475 for the rationale).Changed in version 3.6: Accepts a path-like object.
The following constants are options for the flags parameter to the
open()
function. They can be combined using the bitwise OR operator
|
. Some of them are not available on all platforms. For descriptions of
their availability and use, consult the open(2) manual page on Unix
or the MSDN on Windows.
- os.O_RDONLY¶
- os.O_WRONLY¶
- os.O_RDWR¶
- os.O_APPEND¶
- os.O_CREAT¶
- os.O_EXCL¶
- os.O_TRUNC¶
The above constants are available on Unix and Windows.
- os.O_DSYNC¶
- os.O_RSYNC¶
- os.O_SYNC¶
- os.O_NDELAY¶
- os.O_NONBLOCK¶
- os.O_NOCTTY¶
- os.O_CLOEXEC¶
The above constants are only available on Unix.
Changed in version 3.3: Add
O_CLOEXEC
constant.
- os.O_BINARY¶
- os.O_NOINHERIT¶
- os.O_SHORT_LIVED¶
- os.O_TEMPORARY¶
- os.O_RANDOM¶
- os.O_SEQUENTIAL¶
- os.O_TEXT¶
The above constants are only available on Windows.
- os.O_EVTONLY¶
- os.O_FSYNC¶
- os.O_SYMLINK¶
- os.O_NOFOLLOW_ANY¶
The above constants are only available on macOS.
Changed in version 3.10: Add
O_EVTONLY
,O_FSYNC
,O_SYMLINK
andO_NOFOLLOW_ANY
constants.
- os.O_ASYNC¶
- os.O_DIRECT¶
- os.O_DIRECTORY¶
- os.O_NOFOLLOW¶
- os.O_NOATIME¶
- os.O_PATH¶
- os.O_TMPFILE¶
- os.O_SHLOCK¶
- os.O_EXLOCK¶
The above constants are extensions and not present if they are not defined by the C library.
- os.openpty()¶
Open a new pseudo-terminal pair. Return a pair of file descriptors
(master, slave)
for the pty and the tty, respectively. The new file descriptors are non-inheritable. For a (slightly) more portable approach, use thepty
module.Availability: Unix, not WASI.
Changed in version 3.4: The new file descriptors are now non-inheritable.
- os.pipe()¶
Create a pipe. Return a pair of file descriptors
(r, w)
usable for reading and writing, respectively. The new file descriptor is non-inheritable.Availability: Unix, Windows.
Changed in version 3.4: The new file descriptors are now non-inheritable.
- os.pipe2(flags, /)¶
Create a pipe with flags set atomically. flags can be constructed by ORing together one or more of these values:
O_NONBLOCK
,O_CLOEXEC
. Return a pair of file descriptors(r, w)
usable for reading and writing, respectively.Availability: Unix, not WASI.
Added in version 3.3.
- os.posix_fallocate(fd, offset, len, /)¶
Ensures that enough disk space is allocated for the file specified by fd starting from offset and continuing for len bytes.
Availability: Unix.
Added in version 3.3.
- os.posix_fadvise(fd, offset, len, advice, /)¶
Announces an intention to access data in a specific pattern thus allowing the kernel to make optimizations. The advice applies to the region of the file specified by fd starting at offset and continuing for len bytes. advice is one of
POSIX_FADV_NORMAL
,POSIX_FADV_SEQUENTIAL
,POSIX_FADV_RANDOM
,POSIX_FADV_NOREUSE
,POSIX_FADV_WILLNEED
orPOSIX_FADV_DONTNEED
.Availability: Unix.
Added in version 3.3.
- os.POSIX_FADV_NORMAL¶
- os.POSIX_FADV_SEQUENTIAL¶
- os.POSIX_FADV_RANDOM¶
- os.POSIX_FADV_NOREUSE¶
- os.POSIX_FADV_WILLNEED¶
- os.POSIX_FADV_DONTNEED¶
Flags that can be used in advice in
posix_fadvise()
that specify the access pattern that is likely to be used.Availability: Unix.
Added in version 3.3.
- os.pread(fd, n, offset, /)¶
Read at most n bytes from file descriptor fd at a position of offset, leaving the file offset unchanged.
Return a bytestring containing the bytes read. If the end of the file referred to by fd has been reached, an empty bytes object is returned.
Availability: Unix.
Added in version 3.3.
- os.posix_openpt(oflag, /)¶
Open and return a file descriptor for a master pseudo-terminal device.
Calls the C standard library function
posix_openpt()
. The oflag argument is used to set file status flags and file access modes as specified in the manual page ofposix_openpt()
of your system.The returned file descriptor is non-inheritable. If the value
O_CLOEXEC
is available on the system, it is added to oflag.Availability: Unix, not WASI.
Added in version 3.13.
- os.preadv(fd, buffers, offset, flags=0, /)¶
Read from a file descriptor fd at a position of offset into mutable bytes-like objects buffers, leaving the file offset unchanged. Transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data.
The flags argument contains a bitwise OR of zero or more of the following flags:
Return the total number of bytes actually read which can be less than the total capacity of all the objects.
The operating system may set a limit (
sysconf()
value'SC_IOV_MAX'
) on the number of buffers that can be used.Combine the functionality of
os.readv()
andos.pread()
.Availability: Linux >= 2.6.30, FreeBSD >= 6.0, OpenBSD >= 2.7, AIX >= 7.1.
Using flags requires Linux >= 4.6.
Added in version 3.7.
- os.RWF_NOWAIT¶
Do not wait for data which is not immediately available. If this flag is specified, the system call will return instantly if it would have to read data from the backing storage or wait for a lock.
If some data was successfully read, it will return the number of bytes read. If no bytes were read, it will return
-1
and set errno toerrno.EAGAIN
.Availability: Linux >= 4.14.
Added in version 3.7.
- os.RWF_HIPRI¶
High priority read/write. Allows block-based filesystems to use polling of the device, which provides lower latency, but may use additional resources.
Currently, on Linux, this feature is usable only on a file descriptor opened using the
O_DIRECT
flag.Availability: Linux >= 4.6.
Added in version 3.7.
- os.ptsname(fd, /)¶
Return the name of the slave pseudo-terminal device associated with the master pseudo-terminal device to which the file descriptor fd refers. The file descriptor fd is not closed upon failure.
Calls the reentrant C standard library function
ptsname_r()
if it is available; otherwise, the C standard library functionptsname()
, which is not guaranteed to be thread-safe, is called.Availability: Unix, not WASI.
Added in version 3.13.
- os.pwrite(fd, str, offset, /)¶
Write the bytestring in str to file descriptor fd at position of offset, leaving the file offset unchanged.
Return the number of bytes actually written.
Availability: Unix.
Added in version 3.3.
- os.pwritev(fd, buffers, offset, flags=0, /)¶
Write the buffers contents to file descriptor fd at an offset offset, leaving the file offset unchanged. buffers must be a sequence of bytes-like objects. Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on.
The flags argument contains a bitwise OR of zero or more of the following flags:
Return the total number of bytes actually written.
The operating system may set a limit (
sysconf()
value'SC_IOV_MAX'
) on the number of buffers that can be used.Combine the functionality of
os.writev()
andos.pwrite()
.Availability: Linux >= 2.6.30, FreeBSD >= 6.0, OpenBSD >= 2.7, AIX >= 7.1.
Using flags requires Linux >= 4.6.
Added in version 3.7.
- os.RWF_DSYNC¶
Provide a per-write equivalent of the
O_DSYNC
os.open()
flag. This flag effect applies only to the data range written by the system call.Availability: Linux >= 4.7.
Added in version 3.7.
- os.RWF_SYNC¶
Provide a per-write equivalent of the
O_SYNC
os.open()
flag. This flag effect applies only to the data range written by the system call.Availability: Linux >= 4.7.
Added in version 3.7.
- os.RWF_APPEND¶
Provide a per-write equivalent of the
O_APPEND
os.open()
flag. This flag is meaningful only foros.pwritev()
, and its effect applies only to the data range written by the system call. The offset argument does not affect the write operation; the data is always appended to the end of the file. However, if the offset argument is-1
, the current file offset is updated.Availability: Linux >= 4.16.
Added in version 3.10.
- os.read(fd, n, /)¶
Read at most n bytes from file descriptor fd.
Return a bytestring containing the bytes read. If the end of the file referred to by fd has been reached, an empty bytes object is returned.
Note
This function is intended for low-level I/O and must be applied to a file descriptor as returned by
os.open()
orpipe()
. To read a “file object” returned by the built-in functionopen()
or bypopen()
orfdopen()
, orsys.stdin
, use itsread()
orreadline()
methods.Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an
InterruptedError
exception (see PEP 475 for the rationale).
- os.sendfile(out_fd, in_fd, offset, count)¶
- os.sendfile(out_fd, in_fd, offset, count, headers=(), trailers=(), flags=0)
Copy count bytes from file descriptor in_fd to file descriptor out_fd starting at offset. Return the number of bytes sent. When EOF is reached return
0
.The first function notation is supported by all platforms that define
sendfile()
.On Linux, if offset is given as
None
, the bytes are read from the current position of in_fd and the position of in_fd is updated.The second case may be used on macOS and FreeBSD where headers and trailers are arbitrary sequences of buffers that are written before and after the data from in_fd is written. It returns the same as the first case.
On macOS and FreeBSD, a value of
0
for count specifies to send until the end of in_fd is reached.All platforms support sockets as out_fd file descriptor, and some platforms allow other types (e.g. regular file, pipe) as well.
Cross-platform applications should not use headers, trailers and flags arguments.
Availability: Unix, not WASI.
Note
For a higher-level wrapper of
sendfile()
, seesocket.socket.sendfile()
.Added in version 3.3.
Changed in version 3.9: Parameters out and in was renamed to out_fd and in_fd.
- os.SF_NODISKIO¶
- os.SF_MNOWAIT¶
- os.SF_SYNC¶
Parameters to the
sendfile()
function, if the implementation supports them.Availability: Unix, not WASI.
Added in version 3.3.
- os.SF_NOCACHE¶
Parameter to the
sendfile()
function, if the implementation supports it. The data won’t be cached in the virtual memory and will be freed afterwards.Availability: Unix, not WASI.
Added in version 3.11.
- os.set_blocking(fd, blocking, /)¶
Set the blocking mode of the specified file descriptor. Set the
O_NONBLOCK
flag if blocking isFalse
, clear the flag otherwise.See also
get_blocking()
andsocket.socket.setblocking()
.Availability: Unix, Windows.
The function is limited on WASI, see WebAssembly platforms for more information.
On Windows, this function is limited to pipes.
Added in version 3.5.
Changed in version 3.12: Added support for pipes on Windows.
- os.splice(src, dst, count, offset_src=None, offset_dst=None, flags=0)¶
Transfer count bytes from file descriptor src, starting from offset offset_src, to file descriptor dst, starting from offset offset_dst.
The splicing behaviour can be modified by specifying a flags value. Any of the following variables may used, combined using bitwise OR (the
|
operator):If
SPLICE_F_MOVE
is specified, the kernel is asked to move pages instead of copying, but pages may still be copied if the kernel cannot move the pages from the pipe.If
SPLICE_F_NONBLOCK
is specified, the kernel is asked to not block on I/O. This makes the splice pipe operations nonblocking, but splice may nevertheless block because the spliced file descriptors may block.If
SPLICE_F_MORE
is specified, it hints to the kernel that more data will be coming in a subsequent splice.
At least one of the file descriptors must refer to a pipe. If offset_src is
None
, then src is read from the current position; respectively for offset_dst. The offset associated to the file descriptor that refers to a pipe must beNone
. The files pointed to by src and dst must reside in the same filesystem, otherwise anOSError
is raised witherrno
set toerrno.EXDEV
.This copy is done without the additional cost of transferring data from the kernel to user space and then back into the kernel. Additionally, some filesystems could implement extra optimizations. The copy is done as if both files are opened as binary.
Upon successful completion, returns the number of bytes spliced to or from the pipe. A return value of 0 means end of input. If src refers to a pipe, then this means that there was no data to transfer, and it would not make sense to block because there are no writers connected to the write end of the pipe.
See also
The splice(2) man page.
Availability: Linux >= 2.6.17 with glibc >= 2.5
Added in version 3.10.
- os.readv(fd, buffers, /)¶
Read from a file descriptor fd into a number of mutable bytes-like objects buffers. Transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data.
Return the total number of bytes actually read which can be less than the total capacity of all the objects.
The operating system may set a limit (
sysconf()
value'SC_IOV_MAX'
) on the number of buffers that can be used.Availability: Unix.
Added in version 3.3.
- os.tcgetpgrp(fd, /)¶
Return the process group associated with the terminal given by fd (an open file descriptor as returned by
os.open()
).Availability: Unix, not WASI.
- os.tcsetpgrp(fd, pg, /)¶
Set the process group associated with the terminal given by fd (an open file descriptor as returned by
os.open()
) to pg.Availability: Unix, not WASI.
- os.ttyname(fd, /)¶
Return a string which specifies the terminal device associated with file descriptor fd. If fd is not associated with a terminal device, an exception is raised.
Availability: Unix.
- os.unlockpt(fd, /)¶
Unlock the slave pseudo-terminal device associated with the master pseudo-terminal device to which the file descriptor fd refers. The file descriptor fd is not closed upon failure.
Calls the C standard library function
unlockpt()
.Availability: Unix, not WASI.
Added in version 3.13.
- os.write(fd, str, /)¶
Write the bytestring in str to file descriptor fd.
Return the number of bytes actually written.
Note
This function is intended for low-level I/O and must be applied to a file descriptor as returned by
os.open()
orpipe()
. To write a “file object” returned by the built-in functionopen()
or bypopen()
orfdopen()
, orsys.stdout
orsys.stderr
, use itswrite()
method.Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an
InterruptedError
exception (see PEP 475 for the rationale).
- os.writev(fd, buffers, /)¶
Write the contents of buffers to file descriptor fd. buffers must be a sequence of bytes-like objects. Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on.
Returns the total number of bytes actually written.
The operating system may set a limit (
sysconf()
value'SC_IOV_MAX'
) on the number of buffers that can be used.Availability: Unix.
Added in version 3.3.
Querying the size of a terminal¶
Added in version 3.3.
- os.get_terminal_size(fd=STDOUT_FILENO, /)¶
Return the size of the terminal window as
(columns, lines)
, tuple of typeterminal_size
.The optional argument
fd
(defaultSTDOUT_FILENO
, or standard output) specifies which file descriptor should be queried.If the file descriptor is not connected to a terminal, an
OSError
is raised.shutil.get_terminal_size()
is the high-level function which should normally be used,os.get_terminal_size
is the low-level implementation.Availability: Unix, Windows.
Inheritance of File Descriptors¶
Added in version 3.4.
A file descriptor has an “inheritable” flag which indicates if the file descriptor can be inherited by child processes. Since Python 3.4, file descriptors created by Python are non-inheritable by default.
On UNIX, non-inheritable file descriptors are closed in child processes at the execution of a new program, other file descriptors are inherited.
On Windows, non-inheritable handles and file descriptors are closed in child
processes, except for standard streams (file descriptors 0, 1 and 2: stdin, stdout
and stderr), which are always inherited. Using spawn*
functions,
all inheritable handles and all inheritable file descriptors are inherited.
Using the subprocess
module, all file descriptors except standard
streams are closed, and inheritable handles are only inherited if the
close_fds parameter is False
.
On WebAssembly platforms, the file descriptor cannot be modified.
- os.get_inheritable(fd, /)¶
Get the “inheritable” flag of the specified file descriptor (a boolean).
- os.set_inheritable(fd, inheritable, /)¶
Set the “inheritable” flag of the specified file descriptor.
- os.get_handle_inheritable(handle, /)¶
Get the “inheritable” flag of the specified handle (a boolean).
Availability: Windows.
- os.set_handle_inheritable(handle, inheritable, /)¶
Set the “inheritable” flag of the specified handle.
Availability: Windows.
Files and Directories¶
On some Unix platforms, many of these functions support one or more of these features:
specifying a file descriptor: Normally the path argument provided to functions in the
os
module must be a string specifying a file path. However, some functions now alternatively accept an open file descriptor for their path argument. The function will then operate on the file referred to by the descriptor. (For POSIX systems, Python will call the variant of the function prefixed withf
(e.g. callfchdir
instead ofchdir
).)You can check whether or not path can be specified as a file descriptor for a particular function on your platform using
os.supports_fd
. If this functionality is unavailable, using it will raise aNotImplementedError
.If the function also supports dir_fd or follow_symlinks arguments, it’s an error to specify one of those when supplying path as a file descriptor.
paths relative to directory descriptors: If dir_fd is not
None
, it should be a file descriptor referring to a directory, and the path to operate on should be relative; path will then be relative to that directory. If the path is absolute, dir_fd is ignored. (For POSIX systems, Python will call the variant of the function with anat
suffix and possibly prefixed withf
(e.g. callfaccessat
instead ofaccess
).You can check whether or not dir_fd is supported for a particular function on your platform using
os.supports_dir_fd
. If it’s unavailable, using it will raise aNotImplementedError
.
not following symlinks: If follow_symlinks is
False
, and the last element of the path to operate on is a symbolic link, the function will operate on the symbolic link itself rather than the file pointed to by the link. (For POSIX systems, Python will call thel...
variant of the function.)You can check whether or not follow_symlinks is supported for a particular function on your platform using
os.supports_follow_symlinks
. If it’s unavailable, using it will raise aNotImplementedError
.
- os.access(path, mode, *, dir_fd=None, effective_ids=False, follow_symlinks=True)¶
Use the real uid/gid to test for access to path. Note that most operations will use the effective uid/gid, therefore this routine can be used in a suid/sgid environment to test if the invoking user has the specified access to path. mode should be
F_OK
to test the existence of path, or it can be the inclusive OR of one or more ofR_OK
,W_OK
, andX_OK
to test permissions. ReturnTrue
if access is allowed,False
if not. See the Unix man page access(2) for more information.This function can support specifying paths relative to directory descriptors and not following symlinks.
If effective_ids is
True
,access()
will perform its access checks using the effective uid/gid instead of the real uid/gid. effective_ids may not be supported on your platform; you can check whether or not it is available usingos.supports_effective_ids
. If it is unavailable, using it will raise aNotImplementedError
.Note
Using
access()
to check if a user is authorized to e.g. open a file before actually doing so usingopen()
creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. It’s preferable to use EAFP techniques. For example:if os.access("myfile", os.R_OK): with open("myfile") as fp: return fp.read() return "some default data"
is better written as:
try: fp = open("myfile") except PermissionError: return "some default data" else: with fp: return fp.read()
Note
I/O operations may fail even when
access()
indicates that they would succeed, particularly for operations on network filesystems which may have permissions semantics beyond the usual POSIX permission-bit model.Changed in version 3.3: Added the dir_fd, effective_ids, and follow_symlinks parameters.
Changed in version 3.6: Accepts a path-like object.
- os.F_OK¶
- os.R_OK¶
- os.W_OK¶
- os.X_OK¶
Values to pass as the mode parameter of
access()
to test the existence, readability, writability and executability of path, respectively.
- os.chdir(path)¶
Change the current working directory to path.
This function can support specifying a file descriptor. The descriptor must refer to an opened directory, not an open file.
This function can raise
OSError
and subclasses such asFileNotFoundError
,PermissionError
, andNotADirectoryError
.Raises an auditing event
os.chdir
with argumentpath
.Changed in version 3.3: Added support for specifying path as a file descriptor on some platforms.
Changed in version 3.6: Accepts a path-like object.
- os.chflags(path, flags, *, follow_symlinks=True)¶
Set the flags of path to the numeric flags. flags may take a combination (bitwise OR) of the following values (as defined in the
stat
module):This function can support not following symlinks.
Raises an auditing event
os.chflags
with argumentspath
,flags
.Availability: Unix, not WASI.
Changed in version 3.3: Added the follow_symlinks parameter.
Changed in version 3.6: Accepts a path-like object.
- os.chmod(path, mode, *, dir_fd=None, follow_symlinks=True)¶
Change the mode of path to the numeric mode. mode may take one of the following values (as defined in the
stat
module) or bitwise ORed combinations of them:This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
Note
Although Windows supports
chmod()
, you can only set the file’s read-only flag with it (via thestat.S_IWRITE
andstat.S_IREAD
constants or a corresponding integer value). All other bits are ignored. The default value of follow_symlinks isFalse
on Windows.The function is limited on WASI, see WebAssembly platforms for more information.
Raises an auditing event
os.chmod
with argumentspath
,mode
,dir_fd
.Changed in version 3.3: Added support for specifying path as an open file descriptor, and the dir_fd and follow_symlinks arguments.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.13: Added support for a file descriptor and the follow_symlinks argument on Windows.
- os.chown(path, uid, gid, *, dir_fd=None, follow_symlinks=True)¶
Change the owner and group id of path to the numeric uid and gid. To leave one of the ids unchanged, set it to -1.
This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
See
shutil.chown()
for a higher-level function that accepts names in addition to numeric ids.Raises an auditing event
os.chown
with argumentspath
,uid
,gid
,dir_fd
.Availability: Unix.
The function is limited on WASI, see WebAssembly platforms for more information.
Changed in version 3.3: Added support for specifying path as an open file descriptor, and the dir_fd and follow_symlinks arguments.
Changed in version 3.6: Supports a path-like object.
- os.chroot(path)¶
Change the root directory of the current process to path.
Availability: Unix, not WASI, not Android.
Changed in version 3.6: Accepts a path-like object.
- os.fchdir(fd)¶
Change the current working directory to the directory represented by the file descriptor fd. The descriptor must refer to an opened directory, not an open file. As of Python 3.3, this is equivalent to
os.chdir(fd)
.Raises an auditing event
os.chdir
with argumentpath
.Availability: Unix.
- os.getcwd()¶
Return a string representing the current working directory.
- os.getcwdb()¶
Return a bytestring representing the current working directory.
Changed in version 3.8: The function now uses the UTF-8 encoding on Windows, rather than the ANSI code page: see PEP 529 for the rationale. The function is no longer deprecated on Windows.
- os.lchflags(path, flags)¶
Set the flags of path to the numeric flags, like
chflags()
, but do not follow symbolic links. As of Python 3.3, this is equivalent toos.chflags(path, flags, follow_symlinks=False)
.Raises an auditing event
os.chflags
with argumentspath
,flags
.Availability: Unix, not WASI.
Changed in version 3.6: Accepts a path-like object.
- os.lchmod(path, mode)¶
Change the mode of path to the numeric mode. If path is a symlink, this affects the symlink rather than the target. See the docs for
chmod()
for possible values of mode. As of Python 3.3, this is equivalent toos.chmod(path, mode, follow_symlinks=False)
.lchmod()
is not part of POSIX, but Unix implementations may have it if changing the mode of symbolic links is supported.Raises an auditing event
os.chmod
with argumentspath
,mode
,dir_fd
.Availability: Unix, Windows, not Linux, FreeBSD >= 1.3, NetBSD >= 1.3, not OpenBSD
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.13: Added support on Windows.
- os.lchown(path, uid, gid)¶
Change the owner and group id of path to the numeric uid and gid. This function will not follow symbolic links. As of Python 3.3, this is equivalent to
os.chown(path, uid, gid, follow_symlinks=False)
.Raises an auditing event
os.chown
with argumentspath
,uid
,gid
,dir_fd
.Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
- os.link(src, dst, *, src_dir_fd=None, dst_dir_fd=None, follow_symlinks=True)¶
Create a hard link pointing to src named dst.
This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors, and not following symlinks.
Raises an auditing event
os.link
with argumentssrc
,dst
,src_dir_fd
,dst_dir_fd
.Availability: Unix, Windows.
Changed in version 3.2: Added Windows support.
Changed in version 3.3: Added the src_dir_fd, dst_dir_fd, and follow_symlinks parameters.
Changed in version 3.6: Accepts a path-like object for src and dst.
- os.listdir(path='.')¶
Return a list containing the names of the entries in the directory given by path. The list is in arbitrary order, and does not include the special entries
'.'
and'..'
even if they are present in the directory. If a file is removed from or added to the directory during the call of this function, whether a name for that file be included is unspecified.path may be a path-like object. If path is of type
bytes
(directly or indirectly through thePathLike
interface), the filenames returned will also be of typebytes
; in all other circumstances, they will be of typestr
.This function can also support specifying a file descriptor; the file descriptor must refer to a directory.
Raises an auditing event
os.listdir
with argumentpath
.Note
To encode
str
filenames tobytes
, usefsencode()
.See also
The
scandir()
function returns directory entries along with file attribute information, giving better performance for many common use cases.Changed in version 3.2: The path parameter became optional.
Changed in version 3.3: Added support for specifying path as an open file descriptor.
Changed in version 3.6: Accepts a path-like object.
- os.listdrives()¶
Return a list containing the names of drives on a Windows system.
A drive name typically looks like
'C:\\'
. Not every drive name will be associated with a volume, and some may be inaccessible for a variety of reasons, including permissions, network connectivity or missing media. This function does not test for access.May raise
OSError
if an error occurs collecting the drive names.Raises an auditing event
os.listdrives
with no arguments.Availability: Windows
Added in version 3.12.
- os.listmounts(volume)¶
Return a list containing the mount points for a volume on a Windows system.
volume must be represented as a GUID path, like those returned by
os.listvolumes()
. Volumes may be mounted in multiple locations or not at all. In the latter case, the list will be empty. Mount points that are not associated with a volume will not be returned by this function.The mount points return by this function will be absolute paths, and may be longer than the drive name.
Raises
OSError
if the volume is not recognized or if an error occurs collecting the paths.Raises an auditing event
os.listmounts
with argumentvolume
.Availability: Windows
Added in version 3.12.
- os.listvolumes()¶
Return a list containing the volumes in the system.
Volumes are typically represented as a GUID path that looks like
\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\
. Files can usually be accessed through a GUID path, permissions allowing. However, users are generally not familiar with them, and so the recommended use of this function is to retrieve mount points usingos.listmounts()
.May raise
OSError
if an error occurs collecting the volumes.Raises an auditing event
os.listvolumes
with no arguments.Availability: Windows
Added in version 3.12.
- os.lstat(path, *, dir_fd=None)¶
Perform the equivalent of an
lstat()
system call on the given path. Similar tostat()
, but does not follow symbolic links. Return astat_result
object.On platforms that do not support symbolic links, this is an alias for
stat()
.As of Python 3.3, this is equivalent to
os.stat(path, dir_fd=dir_fd, follow_symlinks=False)
.This function can also support paths relative to directory descriptors.
See also
The
stat()
function.Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.8: On Windows, now opens reparse points that represent another path (name surrogates), including symbolic links and directory junctions. Other kinds of reparse points are resolved by the operating system as for
stat()
.
- os.mkdir(path, mode=0o777, *, dir_fd=None)¶
Create a directory named path with numeric mode mode.
If the directory already exists,
FileExistsError
is raised. If a parent directory in the path does not exist,FileNotFoundError
is raised.On some systems, mode is ignored. Where it is used, the current umask value is first masked out. If bits other than the last 9 (i.e. the last 3 digits of the octal representation of the mode) are set, their meaning is platform-dependent. On some platforms, they are ignored and you should call
chmod()
explicitly to set them.On Windows, a mode of
0o700
is specifically handled to apply access control to the new directory such that only the current user and administrators have access. Other values of mode are ignored.This function can also support paths relative to directory descriptors.
It is also possible to create temporary directories; see the
tempfile
module’stempfile.mkdtemp()
function.Raises an auditing event
os.mkdir
with argumentspath
,mode
,dir_fd
.Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.13: Windows now handles a mode of
0o700
.
- os.makedirs(name, mode=0o777, exist_ok=False)¶
Recursive directory creation function. Like
mkdir()
, but makes all intermediate-level directories needed to contain the leaf directory.The mode parameter is passed to
mkdir()
for creating the leaf directory; see the mkdir() description for how it is interpreted. To set the file permission bits of any newly created parent directories you can set the umask before invokingmakedirs()
. The file permission bits of existing parent directories are not changed.If exist_ok is
False
(the default), aFileExistsError
is raised if the target directory already exists.Note
makedirs()
will become confused if the path elements to create includepardir
(eg. “..” on UNIX systems).This function handles UNC paths correctly.
Raises an auditing event
os.mkdir
with argumentspath
,mode
,dir_fd
.Changed in version 3.2: Added the exist_ok parameter.
Changed in version 3.4.1: Before Python 3.4.1, if exist_ok was
True
and the directory existed,makedirs()
would still raise an error if mode did not match the mode of the existing directory. Since this behavior was impossible to implement safely, it was removed in Python 3.4.1. See bpo-21082.Changed in version 3.6: Accepts a path-like object.
Changed in version 3.7: The mode argument no longer affects the file permission bits of newly created intermediate-level directories.
- os.mkfifo(path, mode=0o666, *, dir_fd=None)¶
Create a FIFO (a named pipe) named path with numeric mode mode. The current umask value is first masked out from the mode.
This function can also support paths relative to directory descriptors.
FIFOs are pipes that can be accessed like regular files. FIFOs exist until they are deleted (for example with
os.unlink()
). Generally, FIFOs are used as rendezvous between “client” and “server” type processes: the server opens the FIFO for reading, and the client opens it for writing. Note thatmkfifo()
doesn’t open the FIFO — it just creates the rendezvous point.Availability: Unix, not WASI.
Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
- os.mknod(path, mode=0o600, device=0, *, dir_fd=None)¶
Create a filesystem node (file, device special file or named pipe) named path. mode specifies both the permissions to use and the type of node to be created, being combined (bitwise OR) with one of
stat.S_IFREG
,stat.S_IFCHR
,stat.S_IFBLK
, andstat.S_IFIFO
(those constants are available instat
). Forstat.S_IFCHR
andstat.S_IFBLK
, device defines the newly created device special file (probably usingos.makedev()
), otherwise it is ignored.This function can also support paths relative to directory descriptors.
Availability: Unix, not WASI.
Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
- os.major(device, /)¶
Extract the device major number from a raw device number (usually the
st_dev
orst_rdev
field fromstat
).
- os.minor(device, /)¶
Extract the device minor number from a raw device number (usually the
st_dev
orst_rdev
field fromstat
).
- os.makedev(major, minor, /)¶
Compose a raw device number from the major and minor device numbers.
- os.pathconf(path, name)¶
Return system configuration information relevant to a named file. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX.1, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given in the
pathconf_names
dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.If name is a string and is not known,
ValueError
is raised. If a specific value for name is not supported by the host system, even if it is included inpathconf_names
, anOSError
is raised witherrno.EINVAL
for the error number.This function can support specifying a file descriptor.
Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
- os.pathconf_names¶
Dictionary mapping names accepted by
pathconf()
andfpathconf()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
- os.readlink(path, *, dir_fd=None)¶
Return a string representing the path to which the symbolic link points. The result may be either an absolute or relative pathname; if it is relative, it may be converted to an absolute pathname using
os.path.join(os.path.dirname(path), result)
.If the path is a string object (directly or indirectly through a
PathLike
interface), the result will also be a string object, and the call may raise a UnicodeDecodeError. If the path is a bytes object (direct or indirectly), the result will be a bytes object.This function can also support paths relative to directory descriptors.
When trying to resolve a path that may contain links, use
realpath()
to properly handle recursion and platform differences.Availability: Unix, Windows.
Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object on Unix.
Changed in version 3.8: Accepts a path-like object and a bytes object on Windows.
Added support for directory junctions, and changed to return the substitution path (which typically includes
\\?\
prefix) rather than the optional “print name” field that was previously returned.
- os.remove(path, *, dir_fd=None)¶
Remove (delete) the file path. If path is a directory, an
OSError
is raised. Usermdir()
to remove directories. If the file does not exist, aFileNotFoundError
is raised.This function can support paths relative to directory descriptors.
On Windows, attempting to remove a file that is in use causes an exception to be raised; on Unix, the directory entry is removed but the storage allocated to the file is not made available until the original file is no longer in use.
This function is semantically identical to
unlink()
.Raises an auditing event
os.remove
with argumentspath
,dir_fd
.Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
- os.removedirs(name)¶
Remove directories recursively. Works like
rmdir()
except that, if the leaf directory is successfully removed,removedirs()
tries to successively remove every parent directory mentioned in path until an error is raised (which is ignored, because it generally means that a parent directory is not empty). For example,os.removedirs('foo/bar/baz')
will first remove the directory'foo/bar/baz'
, and then remove'foo/bar'
and'foo'
if they are empty. RaisesOSError
if the leaf directory could not be successfully removed.Raises an auditing event
os.remove
with argumentspath
,dir_fd
.Changed in version 3.6: Accepts a path-like object.
- os.rename(src, dst, *, src_dir_fd=None, dst_dir_fd=None)¶
Rename the file or directory src to dst. If dst exists, the operation will fail with an
OSError
subclass in a number of cases:On Windows, if dst exists a
FileExistsError
is always raised. The operation may fail if src and dst are on different filesystems. Useshutil.move()
to support moves to a different filesystem.On Unix, if src is a file and dst is a directory or vice-versa, an
IsADirectoryError
or aNotADirectoryError
will be raised respectively. If both are directories and dst is empty, dst will be silently replaced. If dst is a non-empty directory, anOSError
is raised. If both are files, dst will be replaced silently if the user has permission. The operation may fail on some Unix flavors if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.
If you want cross-platform overwriting of the destination, use
replace()
.Raises an auditing event
os.rename
with argumentssrc
,dst
,src_dir_fd
,dst_dir_fd
.Changed in version 3.3: Added the src_dir_fd and dst_dir_fd parameters.
Changed in version 3.6: Accepts a path-like object for src and dst.
- os.renames(old, new)¶
Recursive directory or file renaming function. Works like
rename()
, except creation of any intermediate directories needed to make the new pathname good is attempted first. After the rename, directories corresponding to rightmost path segments of the old name will be pruned away usingremovedirs()
.Note
This function can fail with the new directory structure made if you lack permissions needed to remove the leaf directory or file.
Raises an auditing event
os.rename
with argumentssrc
,dst
,src_dir_fd
,dst_dir_fd
.Changed in version 3.6: Accepts a path-like object for old and new.
- os.replace(src, dst, *, src_dir_fd=None, dst_dir_fd=None)¶
Rename the file or directory src to dst. If dst is a non-empty directory,
OSError
will be raised. If dst exists and is a file, it will be replaced silently if the user has permission. The operation may fail if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.
Raises an auditing event
os.rename
with argumentssrc
,dst
,src_dir_fd
,dst_dir_fd
.Added in version 3.3.
Changed in version 3.6: Accepts a path-like object for src and dst.
- os.rmdir(path, *, dir_fd=None)¶
Remove (delete) the directory path. If the directory does not exist or is not empty, a
FileNotFoundError
or anOSError
is raised respectively. In order to remove whole directory trees,shutil.rmtree()
can be used.This function can support paths relative to directory descriptors.
Raises an auditing event
os.rmdir
with argumentspath
,dir_fd
.Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
- os.scandir(path='.')¶
Return an iterator of
os.DirEntry
objects corresponding to the entries in the directory given by path. The entries are yielded in arbitrary order, and the special entries'.'
and'..'
are not included. If a file is removed from or added to the directory after creating the iterator, whether an entry for that file be included is unspecified.Using
scandir()
instead oflistdir()
can significantly increase the performance of code that also needs file type or file attribute information, becauseos.DirEntry
objects expose this information if the operating system provides it when scanning a directory. Allos.DirEntry
methods may perform a system call, butis_dir()
andis_file()
usually only require a system call for symbolic links;os.DirEntry.stat()
always requires a system call on Unix but only requires one for symbolic links on Windows.path may be a path-like object. If path is of type
bytes
(directly or indirectly through thePathLike
interface), the type of thename
andpath
attributes of eachos.DirEntry
will bebytes
; in all other circumstances, they will be of typestr
.This function can also support specifying a file descriptor; the file descriptor must refer to a directory.
Raises an auditing event
os.scandir
with argumentpath
.The
scandir()
iterator supports the context manager protocol and has the following method:- scandir.close()¶
Close the iterator and free acquired resources.
This is called automatically when the iterator is exhausted or garbage collected, or when an error happens during iterating. However it is advisable to call it explicitly or use the
with
statement.Added in version 3.6.
The following example shows a simple use of
scandir()
to display all the files (excluding directories) in the given path that don’t start with'.'
. Theentry.is_file()
call will generally not make an additional system call:with os.scandir(path) as it: for entry in it: if not entry.name.startswith('.') and entry.is_file(): print(entry.name)
Note
On Unix-based systems,
scandir()
uses the system’s opendir() and readdir() functions. On Windows, it uses the Win32 FindFirstFileW and FindNextFileW functions.Added in version 3.5.
Changed in version 3.6: Added support for the context manager protocol and the
close()
method. If ascandir()
iterator is neither exhausted nor explicitly closed aResourceWarning
will be emitted in its destructor.The function accepts a path-like object.
Changed in version 3.7: Added support for file descriptors on Unix.
- class os.DirEntry¶
Object yielded by
scandir()
to expose the file path and other file attributes of a directory entry.scandir()
will provide as much of this information as possible without making additional system calls. When astat()
orlstat()
system call is made, theos.DirEntry
object will cache the result.os.DirEntry
instances are not intended to be stored in long-lived data structures; if you know the file metadata has changed or if a long time has elapsed since callingscandir()
, callos.stat(entry.path)
to fetch up-to-date information.Because the
os.DirEntry
methods can make operating system calls, they may also raiseOSError
. If you need very fine-grained control over errors, you can catchOSError
when calling one of theos.DirEntry
methods and handle as appropriate.To be directly usable as a path-like object,
os.DirEntry
implements thePathLike
interface.Attributes and methods on a
os.DirEntry
instance are as follows:- name¶
The entry’s base filename, relative to the
scandir()
path argument.The
name
attribute will bebytes
if thescandir()
path argument is of typebytes
andstr
otherwise. Usefsdecode()
to decode byte filenames.
- path¶
The entry’s full path name: equivalent to
os.path.join(scandir_path, entry.name)
where scandir_path is thescandir()
path argument. The path is only absolute if thescandir()
path argument was absolute. If thescandir()
path argument was a file descriptor, thepath
attribute is the same as thename
attribute.The
path
attribute will bebytes
if thescandir()
path argument is of typebytes
andstr
otherwise. Usefsdecode()
to decode byte filenames.
- inode()¶
Return the inode number of the entry.
The result is cached on the
os.DirEntry
object. Useos.stat(entry.path, follow_symlinks=False).st_ino
to fetch up-to-date information.On the first, uncached call, a system call is required on Windows but not on Unix.
- is_dir(*, follow_symlinks=True)¶
Return
True
if this entry is a directory or a symbolic link pointing to a directory; returnFalse
if the entry is or points to any other kind of file, or if it doesn’t exist anymore.If follow_symlinks is
False
, returnTrue
only if this entry is a directory (without following symlinks); returnFalse
if the entry is any other kind of file or if it doesn’t exist anymore.The result is cached on the
os.DirEntry
object, with a separate cache for follow_symlinksTrue
andFalse
. Callos.stat()
along withstat.S_ISDIR()
to fetch up-to-date information.On the first, uncached call, no system call is required in most cases. Specifically, for non-symlinks, neither Windows or Unix require a system call, except on certain Unix file systems, such as network file systems, that return
dirent.d_type == DT_UNKNOWN
. If the entry is a symlink, a system call will be required to follow the symlink unless follow_symlinks isFalse
.This method can raise
OSError
, such asPermissionError
, butFileNotFoundError
is caught and not raised.
- is_file(*, follow_symlinks=True)¶
Return
True
if this entry is a file or a symbolic link pointing to a file; returnFalse
if the entry is or points to a directory or other non-file entry, or if it doesn’t exist anymore.If follow_symlinks is
False
, returnTrue
only if this entry is a file (without following symlinks); returnFalse
if the entry is a directory or other non-file entry, or if it doesn’t exist anymore.The result is cached on the
os.DirEntry
object. Caching, system calls made, and exceptions raised are as peris_dir()
.
- is_symlink()¶
Return
True
if this entry is a symbolic link (even if broken); returnFalse
if the entry points to a directory or any kind of file, or if it doesn’t exist anymore.The result is cached on the
os.DirEntry
object. Callos.path.islink()
to fetch up-to-date information.On the first, uncached call, no system call is required in most cases. Specifically, neither Windows or Unix require a system call, except on certain Unix file systems, such as network file systems, that return
dirent.d_type == DT_UNKNOWN
.This method can raise
OSError
, such asPermissionError
, butFileNotFoundError
is caught and not raised.
- is_junction()¶
Return
True
if this entry is a junction (even if broken); returnFalse
if the entry points to a regular directory, any kind of file, a symlink, or if it doesn’t exist anymore.The result is cached on the
os.DirEntry
object. Callos.path.isjunction()
to fetch up-to-date information.Added in version 3.12.
- stat(*, follow_symlinks=True)¶
Return a
stat_result
object for this entry. This method follows symbolic links by default; to stat a symbolic link add thefollow_symlinks=False
argument.On Unix, this method always requires a system call. On Windows, it only requires a system call if follow_symlinks is
True
and the entry is a reparse point (for example, a symbolic link or directory junction).On Windows, the
st_ino
,st_dev
andst_nlink
attributes of thestat_result
are always set to zero. Callos.stat()
to get these attributes.The result is cached on the
os.DirEntry
object, with a separate cache for follow_symlinksTrue
andFalse
. Callos.stat()
to fetch up-to-date information.
Note that there is a nice correspondence between several attributes and methods of
os.DirEntry
and ofpathlib.Path
. In particular, thename
attribute has the same meaning, as do theis_dir()
,is_file()
,is_symlink()
,is_junction()
, andstat()
methods.Added in version 3.5.
Changed in version 3.6: Added support for the
PathLike
interface. Added support forbytes
paths on Windows.Changed in version 3.12: The
st_ctime
attribute of a stat result is deprecated on Windows. The file creation time is properly available asst_birthtime
, and in the futurest_ctime
may be changed to return zero or the metadata change time, if available.
- os.stat(path, *, dir_fd=None, follow_symlinks=True)¶
Get the status of a file or a file descriptor. Perform the equivalent of a
stat()
system call on the given path. path may be specified as either a string or bytes – directly or indirectly through thePathLike
interface – or as an open file descriptor. Return astat_result
object.This function normally follows symlinks; to stat a symlink add the argument
follow_symlinks=False
, or uselstat()
.This function can support specifying a file descriptor and not following symlinks.
On Windows, passing
follow_symlinks=False
will disable following all name-surrogate reparse points, which includes symlinks and directory junctions. Other types of reparse points that do not resemble links or that the operating system is unable to follow will be opened directly. When following a chain of multiple links, this may result in the original link being returned instead of the non-link that prevented full traversal. To obtain stat results for the final path in this case, use theos.path.realpath()
function to resolve the path name as far as possible and calllstat()
on the result. This does not apply to dangling symlinks or junction points, which will raise the usual exceptions.Example:
>>> import os >>> statinfo = os.stat('somefile.txt') >>> statinfo os.stat_result(st_mode=33188, st_ino=7876932, st_dev=234881026, st_nlink=1, st_uid=501, st_gid=501, st_size=264, st_atime=1297230295, st_mtime=1297230027, st_ctime=1297230027) >>> statinfo.st_size 264
Changed in version 3.3: Added the dir_fd and follow_symlinks parameters, specifying a file descriptor instead of a path.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.8: On Windows, all reparse points that can be resolved by the operating system are now followed, and passing
follow_symlinks=False
disables following all name surrogate reparse points. If the operating system reaches a reparse point that it is not able to follow, stat now returns the information for the original path as iffollow_symlinks=False
had been specified instead of raising an error.
- class os.stat_result¶
Object whose attributes correspond roughly to the members of the
stat
structure. It is used for the result ofos.stat()
,os.fstat()
andos.lstat()
.Attributes:
- st_mode¶
File mode: file type and file mode bits (permissions).
- st_ino¶
Platform dependent, but if non-zero, uniquely identifies the file for a given value of
st_dev
. Typically:the inode number on Unix,
the file index on Windows
- st_dev¶
Identifier of the device on which this file resides.
- st_nlink¶
Number of hard links.
- st_uid¶
User identifier of the file owner.
- st_gid¶
Group identifier of the file owner.
- st_size¶
Size of the file in bytes, if it is a regular file or a symbolic link. The size of a symbolic link is the length of the pathname it contains, without a terminating null byte.
Timestamps:
- st_atime¶
Time of most recent access expressed in seconds.
- st_mtime¶
Time of most recent content modification expressed in seconds.
- st_ctime¶
Time of most recent metadata change expressed in seconds.
Changed in version 3.12:
st_ctime
is deprecated on Windows. Usest_birthtime
for the file creation time. In the future,st_ctime
will contain the time of the most recent metadata change, as for other platforms.
- st_atime_ns¶
Time of most recent access expressed in nanoseconds as an integer.
Added in version 3.3.
- st_mtime_ns¶
Time of most recent content modification expressed in nanoseconds as an integer.
Added in version 3.3.
- st_ctime_ns¶
Time of most recent metadata change expressed in nanoseconds as an integer.
Added in version 3.3.
Changed in version 3.12:
st_ctime_ns
is deprecated on Windows. Usest_birthtime_ns
for the file creation time. In the future,st_ctime
will contain the time of the most recent metadata change, as for other platforms.
- st_birthtime¶
Time of file creation expressed in seconds. This attribute is not always available, and may raise
AttributeError
.Changed in version 3.12:
st_birthtime
is now available on Windows.
- st_birthtime_ns¶
Time of file creation expressed in nanoseconds as an integer. This attribute is not always available, and may raise
AttributeError
.Added in version 3.12.
Note
The exact meaning and resolution of the
st_atime
,st_mtime
,st_ctime
andst_birthtime
attributes depend on the operating system and the file system. For example, on Windows systems using the FAT32 file systems,st_mtime
has 2-second resolution, andst_atime
has only 1-day resolution. See your operating system documentation for details.Similarly, although
st_atime_ns
,st_mtime_ns
,st_ctime_ns
andst_birthtime_ns
are always expressed in nanoseconds, many systems do not provide nanosecond precision. On systems that do provide nanosecond precision, the floating-point object used to storest_atime
,st_mtime
,st_ctime
andst_birthtime
cannot preserve all of it, and as such will be slightly inexact. If you need the exact timestamps you should always usest_atime_ns
,st_mtime_ns
,st_ctime_ns
andst_birthtime_ns
.On some Unix systems (such as Linux), the following attributes may also be available:
- st_blocks¶
Number of 512-byte blocks allocated for file. This may be smaller than
st_size
/512 when the file has holes.
- st_blksize¶
“Preferred” blocksize for efficient file system I/O. Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.
- st_rdev¶
Type of device if an inode device.
- st_flags¶
User defined flags for file.
On other Unix systems (such as FreeBSD), the following attributes may be available (but may be only filled out if root tries to use them):
- st_gen¶
File generation number.
On Solaris and derivatives, the following attributes may also be available:
- st_fstype¶
String that uniquely identifies the type of the filesystem that contains the file.
On macOS systems, the following attributes may also be available:
- st_rsize¶
Real size of the file.
- st_creator¶
Creator of the file.
- st_type¶
File type.
On Windows systems, the following attributes are also available:
- st_file_attributes¶
Windows file attributes:
dwFileAttributes
member of theBY_HANDLE_FILE_INFORMATION
structure returned byGetFileInformationByHandle()
. See theFILE_ATTRIBUTE_* <stat.FILE_ATTRIBUTE_ARCHIVE>
constants in thestat
module.Added in version 3.5.
- st_reparse_tag¶
When
st_file_attributes
has theFILE_ATTRIBUTE_REPARSE_POINT
set, this field contains the tag identifying the type of reparse point. See theIO_REPARSE_TAG_*
constants in thestat
module.
The standard module
stat
defines functions and constants that are useful for extracting information from astat
structure. (On Windows, some items are filled with dummy values.)For backward compatibility, a
stat_result
instance is also accessible as a tuple of at least 10 integers giving the most important (and portable) members of thestat
structure, in the orderst_mode
,st_ino
,st_dev
,st_nlink
,st_uid
,st_gid
,st_size
,st_atime
,st_mtime
,st_ctime
. More items may be added at the end by some implementations. For compatibility with older Python versions, accessingstat_result
as a tuple always returns integers.Changed in version 3.5: Windows now returns the file index as
st_ino
when available.Changed in version 3.7: Added the
st_fstype
member to Solaris/derivatives.Changed in version 3.8: Added the
st_reparse_tag
member on Windows.Changed in version 3.8: On Windows, the
st_mode
member now identifies special files asS_IFCHR
,S_IFIFO
orS_IFBLK
as appropriate.Changed in version 3.12: On Windows,
st_ctime
is deprecated. Eventually, it will contain the last metadata change time, for consistency with other platforms, but for now still contains creation time. Usest_birthtime
for the creation time.On Windows,
st_ino
may now be up to 128 bits, depending on the file system. Previously it would not be above 64 bits, and larger file identifiers would be arbitrarily packed.On Windows,
st_rdev
no longer returns a value. Previously it would contain the same asst_dev
, which was incorrect.Added the
st_birthtime
member on Windows.
- os.statvfs(path)¶
Perform a
statvfs()
system call on the given path. The return value is an object whose attributes describe the filesystem on the given path, and correspond to the members of thestatvfs
structure, namely:f_bsize
,f_frsize
,f_blocks
,f_bfree
,f_bavail
,f_files
,f_ffree
,f_favail
,f_flag
,f_namemax
,f_fsid
.Two module-level constants are defined for the
f_flag
attribute’s bit-flags: ifST_RDONLY
is set, the filesystem is mounted read-only, and ifST_NOSUID
is set, the semantics of setuid/setgid bits are disabled or not supported.Additional module-level constants are defined for GNU/glibc based systems. These are
ST_NODEV
(disallow access to device special files),ST_NOEXEC
(disallow program execution),ST_SYNCHRONOUS
(writes are synced at once),ST_MANDLOCK
(allow mandatory locks on an FS),ST_WRITE
(write on file/directory/symlink),ST_APPEND
(append-only file),ST_IMMUTABLE
(immutable file),ST_NOATIME
(do not update access times),ST_NODIRATIME
(do not update directory access times),ST_RELATIME
(update atime relative to mtime/ctime).This function can support specifying a file descriptor.
Availability: Unix.
Changed in version 3.2: The
ST_RDONLY
andST_NOSUID
constants were added.Changed in version 3.3: Added support for specifying path as an open file descriptor.
Changed in version 3.4: The
ST_NODEV
,ST_NOEXEC
,ST_SYNCHRONOUS
,ST_MANDLOCK
,ST_WRITE
,ST_APPEND
,ST_IMMUTABLE
,ST_NOATIME
,ST_NODIRATIME
, andST_RELATIME
constants were added.Changed in version 3.6: Accepts a path-like object.
Changed in version 3.7: Added the
f_fsid
attribute.
- os.supports_dir_fd¶
A
set
object indicating which functions in theos
module accept an open file descriptor for their dir_fd parameter. Different platforms provide different features, and the underlying functionality Python uses to implement the dir_fd parameter is not available on all platforms Python supports. For consistency’s sake, functions that may support dir_fd always allow specifying the parameter, but will throw an exception if the functionality is used when it’s not locally available. (SpecifyingNone
for dir_fd is always supported on all platforms.)To check whether a particular function accepts an open file descriptor for its dir_fd parameter, use the
in
operator onsupports_dir_fd
. As an example, this expression evaluates toTrue
ifos.stat()
accepts open file descriptors for dir_fd on the local platform:os.stat in os.supports_dir_fd
Currently dir_fd parameters only work on Unix platforms; none of them work on Windows.
Added in version 3.3.
- os.supports_effective_ids¶
A
set
object indicating whetheros.access()
permits specifyingTrue
for its effective_ids parameter on the local platform. (SpecifyingFalse
for effective_ids is always supported on all platforms.) If the local platform supports it, the collection will containos.access()
; otherwise it will be empty.This expression evaluates to
True
ifos.access()
supportseffective_ids=True
on the local platform:os.access in os.supports_effective_ids
Currently effective_ids is only supported on Unix platforms; it does not work on Windows.
Added in version 3.3.
- os.supports_fd¶
A
set
object indicating which functions in theos
module permit specifying their path parameter as an open file descriptor on the local platform. Different platforms provide different features, and the underlying functionality Python uses to accept open file descriptors as path arguments is not available on all platforms Python supports.To determine whether a particular function permits specifying an open file descriptor for its path parameter, use the
in
operator onsupports_fd
. As an example, this expression evaluates toTrue
ifos.chdir()
accepts open file descriptors for path on your local platform:os.chdir in os.supports_fd
Added in version 3.3.
- os.supports_follow_symlinks¶
A
set
object indicating which functions in theos
module acceptFalse
for their follow_symlinks parameter on the local platform. Different platforms provide different features, and the underlying functionality Python uses to implement follow_symlinks is not available on all platforms Python supports. For consistency’s sake, functions that may support follow_symlinks always allow specifying the parameter, but will throw an exception if the functionality is used when it’s not locally available. (SpecifyingTrue
for follow_symlinks is always supported on all platforms.)To check whether a particular function accepts
False
for its follow_symlinks parameter, use thein
operator onsupports_follow_symlinks
. As an example, this expression evaluates toTrue
if you may specifyfollow_symlinks=False
when callingos.stat()
on the local platform:os.stat in os.supports_follow_symlinks
Added in version 3.3.
- os.symlink(src, dst, target_is_directory=False, *, dir_fd=None)¶
Create a symbolic link pointing to src named dst.
On Windows, a symlink represents either a file or a directory, and does not morph to the target dynamically. If the target is present, the type of the symlink will be created to match. Otherwise, the symlink will be created as a directory if target_is_directory is
True
or a file symlink (the default) otherwise. On non-Windows platforms, target_is_directory is ignored.This function can support paths relative to directory descriptors.
Note
On newer versions of Windows 10, unprivileged accounts can create symlinks if Developer Mode is enabled. When Developer Mode is not available/enabled, the SeCreateSymbolicLinkPrivilege privilege is required, or the process must be run as an administrator.
OSError
is raised when the function is called by an unprivileged user.Raises an auditing event
os.symlink
with argumentssrc
,dst
,dir_fd
.Availability: Unix, Windows.
The function is limited on WASI, see WebAssembly platforms for more information.
Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
Changed in version 3.3: Added the dir_fd parameter, and now allow target_is_directory on non-Windows platforms.
Changed in version 3.6: Accepts a path-like object for src and dst.
Changed in version 3.8: Added support for unelevated symlinks on Windows with Developer Mode.
- os.sync()¶
Force write of everything to disk.
Availability: Unix.
Added in version 3.3.
- os.truncate(path, length)¶
Truncate the file corresponding to path, so that it is at most length bytes in size.
This function can support specifying a file descriptor.
Raises an auditing event
os.truncate
with argumentspath
,length
.Availability: Unix, Windows.
Added in version 3.3.
Changed in version 3.5: Added support for Windows
Changed in version 3.6: Accepts a path-like object.
- os.unlink(path, *, dir_fd=None)¶
Remove (delete) the file path. This function is semantically identical to
remove()
; theunlink
name is its traditional Unix name. Please see the documentation forremove()
for further information.Raises an auditing event
os.remove
with argumentspath
,dir_fd
.Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
- os.utime(path, times=None, *, [ns, ]dir_fd=None, follow_symlinks=True)¶
Set the access and modified times of the file specified by path.
utime()
takes two optional parameters, times and ns. These specify the times set on path and are used as follows:If ns is specified, it must be a 2-tuple of the form
(atime_ns, mtime_ns)
where each member is an int expressing nanoseconds.If times is not
None
, it must be a 2-tuple of the form(atime, mtime)
where each member is an int or float expressing seconds.If times is
None
and ns is unspecified, this is equivalent to specifyingns=(atime_ns, mtime_ns)
where both times are the current time.
It is an error to specify tuples for both times and ns.
Note that the exact times you set here may not be returned by a subsequent
stat()
call, depending on the resolution with which your operating system records access and modification times; seestat()
. The best way to preserve exact times is to use the st_atime_ns and st_mtime_ns fields from theos.stat()
result object with the ns parameter toutime()
.This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
Raises an auditing event
os.utime
with argumentspath
,times
,ns
,dir_fd
.Changed in version 3.3: Added support for specifying path as an open file descriptor, and the dir_fd, follow_symlinks, and ns parameters.
Changed in version 3.6: Accepts a path-like object.
- os.walk(top, topdown=True, onerror=None, followlinks=False)¶
Generate the file names in a directory tree by walking the tree either top-down or bottom-up. For each directory in the tree rooted at directory top (including top itself), it yields a 3-tuple
(dirpath, dirnames, filenames)
.dirpath is a string, the path to the directory. dirnames is a list of the names of the subdirectories in dirpath (including symlinks to directories, and excluding
'.'
and'..'
). filenames is a list of the names of the non-directory files in dirpath. Note that the names in the lists contain no path components. To get a full path (which begins with top) to a file or directory in dirpath, doos.path.join(dirpath, name)
. Whether or not the lists are sorted depends on the file system. If a file is removed from or added to the dirpath directory during generating the lists, whether a name for that file be included is unspecified.If optional argument topdown is
True
or not specified, the triple for a directory is generated before the triples for any of its subdirectories (directories are generated top-down). If topdown isFalse
, the triple for a directory is generated after the triples for all of its subdirectories (directories are generated bottom-up). No matter the value of topdown, the list of subdirectories is retrieved before the tuples for the directory and its subdirectories are generated.When topdown is
True
, the caller can modify the dirnames list in-place (perhaps usingdel
or slice assignment), andwalk()
will only recurse into the subdirectories whose names remain in dirnames; this can be used to prune the search, impose a specific order of visiting, or even to informwalk()
about directories the caller creates or renames before it resumeswalk()
again. Modifying dirnames when topdown isFalse
has no effect on the behavior of the walk, because in bottom-up mode the directories in dirnames are generated before dirpath itself is generated.By default, errors from the
scandir()
call are ignored. If optional argument onerror is specified, it should be a function; it will be called with one argument, anOSError
instance. It can report the error to continue with the walk, or raise the exception to abort the walk. Note that the filename is available as thefilename
attribute of the exception object.By default,
walk()
will not walk down into symbolic links that resolve to directories. Set followlinks toTrue
to visit directories pointed to by symlinks, on systems that support them.Note
Be aware that setting followlinks to
True
can lead to infinite recursion if a link points to a parent directory of itself.walk()
does not keep track of the directories it visited already.Note
If you pass a relative pathname, don’t change the current working directory between resumptions of
walk()
.walk()
never changes the current directory, and assumes that its caller doesn’t either.This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn’t look under any CVS subdirectory:
import os from os.path import join, getsize for root, dirs, files in os.walk('python/Lib/email'): print(root, "consumes", end=" ") print(sum(getsize(join(root, name)) for name in files), end=" ") print("bytes in", len(files), "non-directory files") if 'CVS' in dirs: dirs.remove('CVS') # don't visit CVS directories
In the next example (simple implementation of
shutil.rmtree()
), walking the tree bottom-up is essential,rmdir()
doesn’t allow deleting a directory before the directory is empty:# Delete everything reachable from the directory named in "top", # assuming there are no symbolic links. # CAUTION: This is dangerous! For example, if top == '/', it # could delete all your disk files. import os for root, dirs, files in os.walk(top, topdown=False): for name in files: os.remove(os.path.join(root, name)) for name in dirs: os.rmdir(os.path.join(root, name)) os.rmdir(top)
Raises an auditing event
os.walk
with argumentstop
,topdown
,onerror
,followlinks
.Changed in version 3.5: This function now calls
os.scandir()
instead ofos.listdir()
, making it faster by reducing the number of calls toos.stat()
.Changed in version 3.6: Accepts a path-like object.
- os.fwalk(top='.', topdown=True, onerror=None, *, follow_symlinks=False, dir_fd=None)¶
This behaves exactly like
walk()
, except that it yields a 4-tuple(dirpath, dirnames, filenames, dirfd)
, and it supportsdir_fd
.dirpath, dirnames and filenames are identical to
walk()
output, and dirfd is a file descriptor referring to the directory dirpath.This function always supports paths relative to directory descriptors and not following symlinks. Note however that, unlike other functions, the
fwalk()
default value for follow_symlinks isFalse
.Note
Since
fwalk()
yields file descriptors, those are only valid until the next iteration step, so you should duplicate them (e.g. withdup()
) if you want to keep them longer.This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn’t look under any CVS subdirectory:
import os for root, dirs, files, rootfd in os.fwalk('python/Lib/email'): print(root, "consumes", end="") print(sum([os.stat(name, dir_fd=rootfd).st_size for name in files]), end="") print("bytes in", len(files), "non-directory files") if 'CVS' in dirs: dirs.remove('CVS') # don't visit CVS directories
In the next example, walking the tree bottom-up is essential:
rmdir()
doesn’t allow deleting a directory before the directory is empty:# Delete everything reachable from the directory named in "top", # assuming there are no symbolic links. # CAUTION: This is dangerous! For example, if top == '/', it # could delete all your disk files. import os for root, dirs, files, rootfd in os.fwalk(top, topdown=False): for name in files: os.unlink(name, dir_fd=rootfd) for name in dirs: os.rmdir(name, dir_fd=rootfd)
Raises an auditing event
os.fwalk
with argumentstop
,topdown
,onerror
,follow_symlinks
,dir_fd
.Availability: Unix.
Added in version 3.3.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.7: Added support for
bytes
paths.
- os.memfd_create(name[, flags=os.MFD_CLOEXEC])¶
Create an anonymous file and return a file descriptor that refers to it. flags must be one of the
os.MFD_*
constants available on the system (or a bitwise ORed combination of them). By default, the new file descriptor is non-inheritable.The name supplied in name is used as a filename and will be displayed as the target of the corresponding symbolic link in the directory
/proc/self/fd/
. The displayed name is always prefixed withmemfd:
and serves only for debugging purposes. Names do not affect the behavior of the file descriptor, and as such multiple files can have the same name without any side effects.Availability: Linux >= 3.17 with glibc >= 2.27.
Added in version 3.8.
- os.MFD_CLOEXEC¶
- os.MFD_ALLOW_SEALING¶
- os.MFD_HUGETLB¶
- os.MFD_HUGE_SHIFT¶
- os.MFD_HUGE_MASK¶
- os.MFD_HUGE_64KB¶
- os.MFD_HUGE_512KB¶
- os.MFD_HUGE_1MB¶
- os.MFD_HUGE_2MB¶
- os.MFD_HUGE_8MB¶
- os.MFD_HUGE_16MB¶
- os.MFD_HUGE_32MB¶
- os.MFD_HUGE_256MB¶
- os.MFD_HUGE_512MB¶
- os.MFD_HUGE_1GB¶
- os.MFD_HUGE_2GB¶
- os.MFD_HUGE_16GB¶
These flags can be passed to
memfd_create()
.Availability: Linux >= 3.17 with glibc >= 2.27
The
MFD_HUGE*
flags are only available since Linux 4.14.Added in version 3.8.
- os.eventfd(initval[, flags=os.EFD_CLOEXEC])¶
Create and return an event file descriptor. The file descriptors supports raw
read()
andwrite()
with a buffer size of 8,select()
,poll()
and similar. See man page eventfd(2) for more information. By default, the new file descriptor is non-inheritable.initval is the initial value of the event counter. The initial value must be a 32 bit unsigned integer. Please note that the initial value is limited to a 32 bit unsigned int although the event counter is an unsigned 64 bit integer with a maximum value of 264-2.
flags can be constructed from
EFD_CLOEXEC
,EFD_NONBLOCK
, andEFD_SEMAPHORE
.If
EFD_SEMAPHORE
is specified and the event counter is non-zero,eventfd_read()
returns 1 and decrements the counter by one.If
EFD_SEMAPHORE
is not specified and the event counter is non-zero,eventfd_read()
returns the current event counter value and resets the counter to zero.If the event counter is zero and
EFD_NONBLOCK
is not specified,eventfd_read()
blocks.eventfd_write()
increments the event counter. Write blocks if the write operation would increment the counter to a value larger than 264-2.Example:
import os # semaphore with start value '1' fd = os.eventfd(1, os.EFD_SEMAPHORE | os.EFC_CLOEXEC) try: # acquire semaphore v = os.eventfd_read(fd) try: do_work() finally: # release semaphore os.eventfd_write(fd, v) finally: os.close(fd)
Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.10.
- os.eventfd_read(fd)¶
Read value from an
eventfd()
file descriptor and return a 64 bit unsigned int. The function does not verify that fd is aneventfd()
.Availability: Linux >= 2.6.27
Added in version 3.10.
- os.eventfd_write(fd, value)¶
Add value to an
eventfd()
file descriptor. value must be a 64 bit unsigned int. The function does not verify that fd is aneventfd()
.Availability: Linux >= 2.6.27
Added in version 3.10.
- os.EFD_CLOEXEC¶
Set close-on-exec flag for new
eventfd()
file descriptor.Availability: Linux >= 2.6.27
Added in version 3.10.
- os.EFD_NONBLOCK¶
Set
O_NONBLOCK
status flag for neweventfd()
file descriptor.Availability: Linux >= 2.6.27
Added in version 3.10.
- os.EFD_SEMAPHORE¶
Provide semaphore-like semantics for reads from an
eventfd()
file descriptor. On read the internal counter is decremented by one.Availability: Linux >= 2.6.30
Added in version 3.10.
Timer File Descriptors¶
Added in version 3.13.
These functions provide support for Linux’s timer file descriptor API. Naturally, they are all only available on Linux.
- os.timerfd_create(clockid, /, *, flags=0)¶
Create and return a timer file descriptor (timerfd).
The file descriptor returned by
timerfd_create()
supports:The file descriptor’s
read()
method can be called with a buffer size of 8. If the timer has already expired one or more times,read()
returns the number of expirations with the host’s endianness, which may be converted to anint
byint.from_bytes(x, byteorder=sys.byteorder)
.select()
andpoll()
can be used to wait until timer expires and the file descriptor is readable.clockid must be a valid clock ID, as defined in the
time
module:time.CLOCK_BOOTTIME
(Since Linux 3.15 for timerfd_create)
If clockid is
time.CLOCK_REALTIME
, a settable system-wide real-time clock is used. If system clock is changed, timer setting need to be updated. To cancel timer when system clock is changed, seeTFD_TIMER_CANCEL_ON_SET
.If clockid is
time.CLOCK_MONOTONIC
, a non-settable monotonically increasing clock is used. Even if the system clock is changed, the timer setting will not be affected.If clockid is
time.CLOCK_BOOTTIME
, same astime.CLOCK_MONOTONIC
except it includes any time that the system is suspended.The file descriptor’s behaviour can be modified by specifying a flags value. Any of the following variables may used, combined using bitwise OR (the
|
operator):If
TFD_NONBLOCK
is not set as a flag,read()
blocks until the timer expires. If it is set as a flag,read()
doesn’t block, but If there hasn’t been an expiration since the last call to read,read()
raisesOSError
witherrno
is set toerrno.EAGAIN
.TFD_CLOEXEC
is always set by Python automatically.The file descriptor must be closed with
os.close()
when it is no longer needed, or else the file descriptor will be leaked.See also
The timerfd_create(2) man page.
Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.timerfd_settime(fd, /, *, flags=flags, initial=0.0, interval=0.0)¶
Alter a timer file descriptor’s internal timer. This function operates the same interval timer as
timerfd_settime_ns()
.fd must be a valid timer file descriptor.
The timer’s behaviour can be modified by specifying a flags value. Any of the following variables may used, combined using bitwise OR (the
|
operator):The timer is disabled by setting initial to zero (
0
). If initial is equal to or greater than zero, the timer is enabled. If initial is less than zero, it raises anOSError
exception witherrno
set toerrno.EINVAL
By default the timer will fire when initial seconds have elapsed. (If initial is zero, timer will fire immediately.)
However, if the
TFD_TIMER_ABSTIME
flag is set, the timer will fire when the timer’s clock (set by clockid intimerfd_create()
) reaches initial seconds.The timer’s interval is set by the interval
float
. If interval is zero, the timer only fires once, on the initial expiration. If interval is greater than zero, the timer fires every time interval seconds have elapsed since the previous expiration. If interval is less than zero, it raisesOSError
witherrno
set toerrno.EINVAL
If the
TFD_TIMER_CANCEL_ON_SET
flag is set along withTFD_TIMER_ABSTIME
and the clock for this timer istime.CLOCK_REALTIME
, the timer is marked as cancelable if the real-time clock is changed discontinuously. Reading the descriptor is aborted with the error ECANCELED.Linux manages system clock as UTC. A daylight-savings time transition is done by changing time offset only and doesn’t cause discontinuous system clock change.
Discontinuous system clock change will be caused by the following events:
settimeofday
clock_settime
set the system date and time by
date
command
Return a two-item tuple of (
next_expiration
,interval
) from the previous timer state, before this function executed.See also
timerfd_create(2), timerfd_settime(2), settimeofday(2), clock_settime(2), and date(1).
Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.timerfd_settime_ns(fd, /, *, flags=0, initial=0, interval=0)¶
Similar to
timerfd_settime()
, but use time as nanoseconds. This function operates the same interval timer astimerfd_settime()
.Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.timerfd_gettime(fd, /)¶
Return a two-item tuple of floats (
next_expiration
,interval
).next_expiration
denotes the relative time until next the timer next fires, regardless of if theTFD_TIMER_ABSTIME
flag is set.interval
denotes the timer’s interval. If zero, the timer will only fire once, afternext_expiration
seconds have elapsed.See also
Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.timerfd_gettime_ns(fd, /)¶
Similar to
timerfd_gettime()
, but return time as nanoseconds.Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.TFD_NONBLOCK¶
A flag for the
timerfd_create()
function, which sets theO_NONBLOCK
status flag for the new timer file descriptor. IfTFD_NONBLOCK
is not set as a flag,read()
blocks.Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.TFD_CLOEXEC¶
A flag for the
timerfd_create()
function, IfTFD_CLOEXEC
is set as a flag, set close-on-exec flag for new file descriptor.Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.TFD_TIMER_ABSTIME¶
A flag for the
timerfd_settime()
andtimerfd_settime_ns()
functions. If this flag is set, initial is interpreted as an absolute value on the timer’s clock (in UTC seconds or nanoseconds since the Unix Epoch).Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
- os.TFD_TIMER_CANCEL_ON_SET¶
A flag for the
timerfd_settime()
andtimerfd_settime_ns()
functions along withTFD_TIMER_ABSTIME
. The timer is cancelled when the time of the underlying clock changes discontinuously.Availability: Linux >= 2.6.27 with glibc >= 2.8
Added in version 3.13.
Linux extended attributes¶
Added in version 3.3.
These functions are all available on Linux only.
- os.getxattr(path, attribute, *, follow_symlinks=True)¶
Return the value of the extended filesystem attribute attribute for path. attribute can be bytes or str (directly or indirectly through the
PathLike
interface). If it is str, it is encoded with the filesystem encoding.This function can support specifying a file descriptor and not following symlinks.
Raises an auditing event
os.getxattr
with argumentspath
,attribute
.Changed in version 3.6: Accepts a path-like object for path and attribute.
- os.listxattr(path=None, *, follow_symlinks=True)¶
Return a list of the extended filesystem attributes on path. The attributes in the list are represented as strings decoded with the filesystem encoding. If path is
None
,listxattr()
will examine the current directory.This function can support specifying a file descriptor and not following symlinks.
Raises an auditing event
os.listxattr
with argumentpath
.Changed in version 3.6: Accepts a path-like object.
- os.removexattr(path, attribute, *, follow_symlinks=True)¶
Removes the extended filesystem attribute attribute from path. attribute should be bytes or str (directly or indirectly through the
PathLike
interface). If it is a string, it is encoded with the filesystem encoding and error handler.This function can support specifying a file descriptor and not following symlinks.
Raises an auditing event
os.removexattr
with argumentspath
,attribute
.Changed in version 3.6: Accepts a path-like object for path and attribute.
- os.setxattr(path, attribute, value, flags=0, *, follow_symlinks=True)¶
Set the extended filesystem attribute attribute on path to value. attribute must be a bytes or str with no embedded NULs (directly or indirectly through the
PathLike
interface). If it is a str, it is encoded with the filesystem encoding and error handler. flags may beXATTR_REPLACE
orXATTR_CREATE
. IfXATTR_REPLACE
is given and the attribute does not exist,ENODATA
will be raised. IfXATTR_CREATE
is given and the attribute already exists, the attribute will not be created andEEXISTS
will be raised.This function can support specifying a file descriptor and not following symlinks.
Note
A bug in Linux kernel versions less than 2.6.39 caused the flags argument to be ignored on some filesystems.
Raises an auditing event
os.setxattr
with argumentspath
,attribute
,value
,flags
.Changed in version 3.6: Accepts a path-like object for path and attribute.
- os.XATTR_SIZE_MAX¶
The maximum size the value of an extended attribute can be. Currently, this is 64 KiB on Linux.
- os.XATTR_CREATE¶
This is a possible value for the flags argument in
setxattr()
. It indicates the operation must create an attribute.
- os.XATTR_REPLACE¶
This is a possible value for the flags argument in
setxattr()
. It indicates the operation must replace an existing attribute.
Process Management¶
These functions may be used to create and manage processes.
The various exec*
functions take a list of arguments for the new
program loaded into the process. In each case, the first of these arguments is
passed to the new program as its own name rather than as an argument a user may
have typed on a command line. For the C programmer, this is the argv[0]
passed to a program’s main()
. For example, os.execv('/bin/echo',
['foo', 'bar'])
will only print bar
on standard output; foo
will seem
to be ignored.
- os.abort()¶
Generate a
SIGABRT
signal to the current process. On Unix, the default behavior is to produce a core dump; on Windows, the process immediately returns an exit code of3
. Be aware that calling this function will not call the Python signal handler registered forSIGABRT
withsignal.signal()
.
- os.add_dll_directory(path)¶
Add a path to the DLL search path.
This search path is used when resolving dependencies for imported extension modules (the module itself is resolved through
sys.path
), and also byctypes
.Remove the directory by calling close() on the returned object or using it in a
with
statement.See the Microsoft documentation for more information about how DLLs are loaded.
Raises an auditing event
os.add_dll_directory
with argumentpath
.Availability: Windows.
Added in version 3.8: Previous versions of CPython would resolve DLLs using the default behavior for the current process. This led to inconsistencies, such as only sometimes searching
PATH
or the current working directory, and OS functions such asAddDllDirectory
having no effect.In 3.8, the two primary ways DLLs are loaded now explicitly override the process-wide behavior to ensure consistency. See the porting notes for information on updating libraries.
- os.execl(path, arg0, arg1, ...)¶
- os.execle(path, arg0, arg1, ..., env)¶
- os.execlp(file, arg0, arg1, ...)¶
- os.execlpe(file, arg0, arg1, ..., env)¶
- os.execv(path, args)¶
- os.execve(path, args, env)¶
- os.execvp(file, args)¶
- os.execvpe(file, args, env)¶
These functions all execute a new program, replacing the current process; they do not return. On Unix, the new executable is loaded into the current process, and will have the same process id as the caller. Errors will be reported as
OSError
exceptions.The current process is replaced immediately. Open file objects and descriptors are not flushed, so if there may be data buffered on these open files, you should flush them using
sys.stdout.flush()
oros.fsync()
before calling anexec*
function.The “l” and “v” variants of the
exec*
functions differ in how command-line arguments are passed. The “l” variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to theexecl*()
functions. The “v” variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process should start with the name of the command being run, but this is not enforced.The variants which include a “p” near the end (
execlp()
,execlpe()
,execvp()
, andexecvpe()
) will use thePATH
environment variable to locate the program file. When the environment is being replaced (using one of theexec*e
variants, discussed in the next paragraph), the new environment is used as the source of thePATH
variable. The other variants,execl()
,execle()
,execv()
, andexecve()
, will not use thePATH
variable to locate the executable; path must contain an appropriate absolute or relative path. Relative paths must include at least one slash, even on Windows, as plain names will not be resolved.For
execle()
,execlpe()
,execve()
, andexecvpe()
(note that these all end in “e”), the env parameter must be a mapping which is used to define the environment variables for the new process (these are used instead of the current process’ environment); the functionsexecl()
,execlp()
,execv()
, andexecvp()
all cause the new process to inherit the environment of the current process.For
execve()
on some platforms, path may also be specified as an open file descriptor. This functionality may not be supported on your platform; you can check whether or not it is available usingos.supports_fd
. If it is unavailable, using it will raise aNotImplementedError
.Raises an auditing event
os.exec
with argumentspath
,args
,env
.Availability: Unix, Windows, not WASI, not Android, not iOS.
Changed in version 3.3: Added support for specifying path as an open file descriptor for
execve()
.Changed in version 3.6: Accepts a path-like object.
- os._exit(n)¶
Exit the process with status n, without calling cleanup handlers, flushing stdio buffers, etc.
Note
The standard way to exit is
sys.exit(n)
._exit()
should normally only be used in the child process after afork()
.
The following exit codes are defined and can be used with _exit()
,
although they are not required. These are typically used for system programs
written in Python, such as a mail server’s external command delivery program.
Note
Some of these may not be available on all Unix platforms, since there is some variation. These constants are defined where they are defined by the underlying platform.
- os.EX_OK¶
Exit code that means no error occurred. May be taken from the defined value of
EXIT_SUCCESS
on some platforms. Generally has a value of zero.Availability: Unix, Windows.
- os.EX_USAGE¶
Exit code that means the command was used incorrectly, such as when the wrong number of arguments are given.
Availability: Unix, not WASI.
- os.EX_DATAERR¶
Exit code that means the input data was incorrect.
Availability: Unix, not WASI.
- os.EX_NOINPUT¶
Exit code that means an input file did not exist or was not readable.
Availability: Unix, not WASI.
- os.EX_NOUSER¶
Exit code that means a specified user did not exist.
Availability: Unix, not WASI.
- os.EX_NOHOST¶
Exit code that means a specified host did not exist.
Availability: Unix, not WASI.
- os.EX_UNAVAILABLE¶
Exit code that means that a required service is unavailable.
Availability: Unix, not WASI.
- os.EX_SOFTWARE¶
Exit code that means an internal software error was detected.
Availability: Unix, not WASI.
- os.EX_OSERR¶
Exit code that means an operating system error was detected, such as the inability to fork or create a pipe.
Availability: Unix, not WASI.
- os.EX_OSFILE¶
Exit code that means some system file did not exist, could not be opened, or had some other kind of error.
Availability: Unix, not WASI.
- os.EX_CANTCREAT¶
Exit code that means a user specified output file could not be created.
Availability: Unix, not WASI.
- os.EX_IOERR¶
Exit code that means that an error occurred while doing I/O on some file.
Availability: Unix, not WASI.
- os.EX_TEMPFAIL¶
Exit code that means a temporary failure occurred. This indicates something that may not really be an error, such as a network connection that couldn’t be made during a retryable operation.
Availability: Unix, not WASI.
- os.EX_PROTOCOL¶
Exit code that means that a protocol exchange was illegal, invalid, or not understood.
Availability: Unix, not WASI.
- os.EX_NOPERM¶
Exit code that means that there were insufficient permissions to perform the operation (but not intended for file system problems).
Availability: Unix, not WASI.
- os.EX_CONFIG¶
Exit code that means that some kind of configuration error occurred.
Availability: Unix, not WASI.
- os.EX_NOTFOUND¶
Exit code that means something like “an entry was not found”.
Availability: Unix, not WASI.
- os.fork()¶
Fork a child process. Return
0
in the child and the child’s process id in the parent. If an error occursOSError
is raised.Note that some platforms including FreeBSD <= 6.3 and Cygwin have known issues when using
fork()
from a thread.Raises an auditing event
os.fork
with no arguments.Warning
If you use TLS sockets in an application calling
fork()
, see the warning in thessl
documentation.Warning
On macOS the use of this function is unsafe when mixed with using higher-level system APIs, and that includes using
urllib.request
.Changed in version 3.8: Calling
fork()
in a subinterpreter is no longer supported (RuntimeError
is raised).Changed in version 3.12: If Python is able to detect that your process has multiple threads,
os.fork()
now raises aDeprecationWarning
.We chose to surface this as a warning, when detectable, to better inform developers of a design problem that the POSIX platform specifically notes as not supported. Even in code that appears to work, it has never been safe to mix threading with
os.fork()
on POSIX platforms. The CPython runtime itself has always made API calls that are not safe for use in the child process when threads existed in the parent (such asmalloc
andfree
).Users of macOS or users of libc or malloc implementations other than those typically found in glibc to date are among those already more likely to experience deadlocks running such code.
See this discussion on fork being incompatible with threads for technical details of why we’re surfacing this longstanding platform compatibility problem to developers.
Availability: POSIX, not WASI, not Android, not iOS.
- os.forkpty()¶
Fork a child process, using a new pseudo-terminal as the child’s controlling terminal. Return a pair of
(pid, fd)
, where pid is0
in the child, the new child’s process id in the parent, and fd is the file descriptor of the master end of the pseudo-terminal. For a more portable approach, use thepty
module. If an error occursOSError
is raised.Raises an auditing event
os.forkpty
with no arguments.Warning
On macOS the use of this function is unsafe when mixed with using higher-level system APIs, and that includes using
urllib.request
.Changed in version 3.8: Calling
forkpty()
in a subinterpreter is no longer supported (RuntimeError
is raised).Changed in version 3.12: If Python is able to detect that your process has multiple threads, this now raises a
DeprecationWarning
. See the longer explanation onos.fork()
.Availability: Unix, not WASI, not Android, not iOS.
- os.kill(pid, sig, /)¶
Send signal sig to the process pid. Constants for the specific signals available on the host platform are defined in the
signal
module.Windows: The
signal.CTRL_C_EVENT
andsignal.CTRL_BREAK_EVENT
signals are special signals which can only be sent to console processes which share a common console window, e.g., some subprocesses. Any other value for sig will cause the process to be unconditionally killed by the TerminateProcess API, and the exit code will be set to sig. The Windows version ofkill()
additionally takes process handles to be killed.See also
signal.pthread_kill()
.Raises an auditing event
os.kill
with argumentspid
,sig
.Availability: Unix, Windows, not WASI, not iOS.
Changed in version 3.2: Added Windows support.
- os.killpg(pgid, sig, /)¶
Send the signal sig to the process group pgid.
Raises an auditing event
os.killpg
with argumentspgid
,sig
.Availability: Unix, not WASI, not iOS.
- os.nice(increment, /)¶
Add increment to the process’s “niceness”. Return the new niceness.
Availability: Unix, not WASI.
- os.pidfd_open(pid, flags=0)¶
Return a file descriptor referring to the process pid with flags set. This descriptor can be used to perform process management without races and signals.
See the pidfd_open(2) man page for more details.
Availability: Linux >= 5.3, Android >=
build-time
API level 31Added in version 3.9.
- os.PIDFD_NONBLOCK¶
This flag indicates that the file descriptor will be non-blocking. If the process referred to by the file descriptor has not yet terminated, then an attempt to wait on the file descriptor using waitid(2) will immediately return the error
EAGAIN
rather than blocking.
Availability: Linux >= 5.10
Added in version 3.12.
- os.plock(op, /)¶
Lock program segments into memory. The value of op (defined in
<sys/lock.h>
) determines which segments are locked.Availability: Unix, not WASI, not iOS.
- os.popen(cmd, mode='r', buffering=-1)¶
Open a pipe to or from command cmd. The return value is an open file object connected to the pipe, which can be read or written depending on whether mode is
'r'
(default) or'w'
. The buffering argument have the same meaning as the corresponding argument to the built-inopen()
function. The returned file object reads or writes text strings rather than bytes.The
close
method returnsNone
if the subprocess exited successfully, or the subprocess’s return code if there was an error. On POSIX systems, if the return code is positive it represents the return value of the process left-shifted by one byte. If the return code is negative, the process was terminated by the signal given by the negated value of the return code. (For example, the return value might be- signal.SIGKILL
if the subprocess was killed.) On Windows systems, the return value contains the signed integer return code from the child process.On Unix,
waitstatus_to_exitcode()
can be used to convert theclose
method result (exit status) into an exit code if it is notNone
. On Windows, theclose
method result is directly the exit code (orNone
).This is implemented using
subprocess.Popen
; see that class’s documentation for more powerful ways to manage and communicate with subprocesses.Availability: not WASI, not Android, not iOS.
Note
The Python UTF-8 Mode affects encodings used for cmd and pipe contents.
popen()
is a simple wrapper aroundsubprocess.Popen
. Usesubprocess.Popen
orsubprocess.run()
to control options like encodings.Deprecated since version 3.14: The function is soft deprecated and should no longer be used to write new code. The
subprocess
module is recommended instead.
- os.posix_spawn(path, argv, env, *, file_actions=None, setpgroup=None, resetids=False, setsid=False, setsigmask=(), setsigdef=(), scheduler=None)¶
Wraps the
posix_spawn()
C library API for use from Python.Most users should use
subprocess.run()
instead ofposix_spawn()
.The positional-only arguments path, args, and env are similar to
execve()
. env is allowed to beNone
, in which case current process’ environment is used.The path parameter is the path to the executable file. The path should contain a directory. Use
posix_spawnp()
to pass an executable file without directory.The file_actions argument may be a sequence of tuples describing actions to take on specific file descriptors in the child process between the C library implementation’s
fork()
andexec()
steps. The first item in each tuple must be one of the three type indicator listed below describing the remaining tuple elements:- os.POSIX_SPAWN_OPEN¶
(
os.POSIX_SPAWN_OPEN
, fd, path, flags, mode)Performs
os.dup2(os.open(path, flags, mode), fd)
.
- os.POSIX_SPAWN_CLOSE¶
(
os.POSIX_SPAWN_CLOSE
, fd)Performs
os.close(fd)
.
- os.POSIX_SPAWN_DUP2¶
(
os.POSIX_SPAWN_DUP2
, fd, new_fd)Performs
os.dup2(fd, new_fd)
.
- os.POSIX_SPAWN_CLOSEFROM¶
(
os.POSIX_SPAWN_CLOSEFROM
, fd)Performs
os.closerange(fd, INF)
.
These tuples correspond to the C library
posix_spawn_file_actions_addopen()
,posix_spawn_file_actions_addclose()
,posix_spawn_file_actions_adddup2()
, andposix_spawn_file_actions_addclosefrom_np()
API calls used to prepare for theposix_spawn()
call itself.The setpgroup argument will set the process group of the child to the value specified. If the value specified is 0, the child’s process group ID will be made the same as its process ID. If the value of setpgroup is not set, the child will inherit the parent’s process group ID. This argument corresponds to the C library
POSIX_SPAWN_SETPGROUP
flag.If the resetids argument is
True
it will reset the effective UID and GID of the child to the real UID and GID of the parent process. If the argument isFalse
, then the child retains the effective UID and GID of the parent. In either case, if the set-user-ID and set-group-ID permission bits are enabled on the executable file, their effect will override the setting of the effective UID and GID. This argument corresponds to the C libraryPOSIX_SPAWN_RESETIDS
flag.If the setsid argument is
True
, it will create a new session ID forposix_spawn
. setsid requiresPOSIX_SPAWN_SETSID
orPOSIX_SPAWN_SETSID_NP
flag. Otherwise,NotImplementedError
is raised.The setsigmask argument will set the signal mask to the signal set specified. If the parameter is not used, then the child inherits the parent’s signal mask. This argument corresponds to the C library
POSIX_SPAWN_SETSIGMASK
flag.The sigdef argument will reset the disposition of all signals in the set specified. This argument corresponds to the C library
POSIX_SPAWN_SETSIGDEF
flag.The scheduler argument must be a tuple containing the (optional) scheduler policy and an instance of
sched_param
with the scheduler parameters. A value ofNone
in the place of the scheduler policy indicates that is not being provided. This argument is a combination of the C libraryPOSIX_SPAWN_SETSCHEDPARAM
andPOSIX_SPAWN_SETSCHEDULER
flags.Raises an auditing event
os.posix_spawn
with argumentspath
,argv
,env
.Added in version 3.8.
Changed in version 3.13: env parameter accepts
None
.os.POSIX_SPAWN_CLOSEFROM
is available on platforms whereposix_spawn_file_actions_addclosefrom_np()
exists.Availability: Unix, not WASI, not Android, not iOS.
- os.posix_spawnp(path, argv, env, *, file_actions=None, setpgroup=None, resetids=False, setsid=False, setsigmask=(), setsigdef=(), scheduler=None)¶
Wraps the
posix_spawnp()
C library API for use from Python.Similar to
posix_spawn()
except that the system searches for the executable file in the list of directories specified by thePATH
environment variable (in the same way as forexecvp(3)
).Raises an auditing event
os.posix_spawn
with argumentspath
,argv
,env
.Added in version 3.8.
Availability: POSIX, not WASI, not Android, not iOS.
See
posix_spawn()
documentation.
- os.register_at_fork(*, before=None, after_in_parent=None, after_in_child=None)¶
Register callables to be executed when a new child process is forked using
os.fork()
or similar process cloning APIs. The parameters are optional and keyword-only. Each specifies a different call point.before is a function called before forking a child process.
after_in_parent is a function called from the parent process after forking a child process.
after_in_child is a function called from the child process.
These calls are only made if control is expected to return to the Python interpreter. A typical
subprocess
launch will not trigger them as the child is not going to re-enter the interpreter.Functions registered for execution before forking are called in reverse registration order. Functions registered for execution after forking (either in the parent or in the child) are called in registration order.
Note that
fork()
calls made by third-party C code may not call those functions, unless it explicitly callsPyOS_BeforeFork()
,PyOS_AfterFork_Parent()
andPyOS_AfterFork_Child()
.There is no way to unregister a function.
Availability: Unix, not WASI, not Android, not iOS.
Added in version 3.7.
- os.spawnl(mode, path, ...)¶
- os.spawnle(mode, path, ..., env)¶
- os.spawnlp(mode, file, ...)¶
- os.spawnlpe(mode, file, ..., env)¶
- os.spawnv(mode, path, args)¶
- os.spawnve(mode, path, args, env)¶
- os.spawnvp(mode, file, args)¶
- os.spawnvpe(mode, file, args, env)¶
Execute the program path in a new process.
(Note that the
subprocess
module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using these functions. Check especially the Replacing Older Functions with the subprocess Module section.)If mode is
P_NOWAIT
, this function returns the process id of the new process; if mode isP_WAIT
, returns the process’s exit code if it exits normally, or-signal
, where signal is the signal that killed the process. On Windows, the process id will actually be the process handle, so can be used with thewaitpid()
function.Note on VxWorks, this function doesn’t return
-signal
when the new process is killed. Instead it raises OSError exception.The “l” and “v” variants of the
spawn*
functions differ in how command-line arguments are passed. The “l” variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to thespawnl*()
functions. The “v” variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process must start with the name of the command being run.The variants which include a second “p” near the end (
spawnlp()
,spawnlpe()
,spawnvp()
, andspawnvpe()
) will use thePATH
environment variable to locate the program file. When the environment is being replaced (using one of thespawn*e
variants, discussed in the next paragraph), the new environment is used as the source of thePATH
variable. The other variants,spawnl()
,spawnle()
,spawnv()
, andspawnve()
, will not use thePATH
variable to locate the executable; path must contain an appropriate absolute or relative path.For
spawnle()
,spawnlpe()
,spawnve()
, andspawnvpe()
(note that these all end in “e”), the env parameter must be a mapping which is used to define the environment variables for the new process (they are used instead of the current process’ environment); the functionsspawnl()
,spawnlp()
,spawnv()
, andspawnvp()
all cause the new process to inherit the environment of the current process. Note that keys and values in the env dictionary must be strings; invalid keys or values will cause the function to fail, with a return value of127
.As an example, the following calls to
spawnlp()
andspawnvpe()
are equivalent:import os os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null') L = ['cp', 'index.html', '/dev/null'] os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)
Raises an auditing event
os.spawn
with argumentsmode
,path
,args
,env
.Availability: Unix, Windows, not WASI, not Android, not iOS.
spawnlp()
,spawnlpe()
,spawnvp()
andspawnvpe()
are not available on Windows.spawnle()
andspawnve()
are not thread-safe on Windows; we advise you to use thesubprocess
module instead.Changed in version 3.6: Accepts a path-like object.
Deprecated since version 3.14: These functions are soft deprecated and should no longer be used to write new code. The
subprocess
module is recommended instead.
- os.P_NOWAIT¶
- os.P_NOWAITO¶
Possible values for the mode parameter to the
spawn*
family of functions. If either of these values is given, thespawn*
functions will return as soon as the new process has been created, with the process id as the return value.Availability: Unix, Windows.
- os.P_WAIT¶
Possible value for the mode parameter to the
spawn*
family of functions. If this is given as mode, thespawn*
functions will not return until the new process has run to completion and will return the exit code of the process the run is successful, or-signal
if a signal kills the process.Availability: Unix, Windows.
- os.P_DETACH¶
- os.P_OVERLAY¶
Possible values for the mode parameter to the
spawn*
family of functions. These are less portable than those listed above.P_DETACH
is similar toP_NOWAIT
, but the new process is detached from the console of the calling process. IfP_OVERLAY
is used, the current process will be replaced; thespawn*
function will not return.Availability: Windows.
- os.startfile(path[, operation][, arguments][, cwd][, show_cmd])¶
Start a file with its associated application.
When operation is not specified, this acts like double-clicking the file in Windows Explorer, or giving the file name as an argument to the start command from the interactive command shell: the file is opened with whatever application (if any) its extension is associated.
When another operation is given, it must be a “command verb” that specifies what should be done with the file. Common verbs documented by Microsoft are
'open'
,'print'
and'edit'
(to be used on files) as well as'explore'
and'find'
(to be used on directories).When launching an application, specify arguments to be passed as a single string. This argument may have no effect when using this function to launch a document.
The default working directory is inherited, but may be overridden by the cwd argument. This should be an absolute path. A relative path will be resolved against this argument.
Use show_cmd to override the default window style. Whether this has any effect will depend on the application being launched. Values are integers as supported by the Win32
ShellExecute()
function.startfile()
returns as soon as the associated application is launched. There is no option to wait for the application to close, and no way to retrieve the application’s exit status. The path parameter is relative to the current directory or cwd. If you want to use an absolute path, make sure the first character is not a slash ('/'
) Usepathlib
or theos.path.normpath()
function to ensure that paths are properly encoded for Win32.To reduce interpreter startup overhead, the Win32
ShellExecute()
function is not resolved until this function is first called. If the function cannot be resolved,NotImplementedError
will be raised.Raises an auditing event
os.startfile
with argumentspath
,operation
.Raises an auditing event
os.startfile/2
with argumentspath
,operation
,arguments
,cwd
,show_cmd
.Availability: Windows.
Changed in version 3.10: Added the arguments, cwd and show_cmd arguments, and the
os.startfile/2
audit event.
- os.system(command)¶
Execute the command (a string) in a subshell. This is implemented by calling the Standard C function
system()
, and has the same limitations. Changes tosys.stdin
, etc. are not reflected in the environment of the executed command. If command generates any output, it will be sent to the interpreter standard output stream. The C standard does not specify the meaning of the return value of the C function, so the return value of the Python function is system-dependent.On Unix, the return value is the exit status of the process encoded in the format specified for
wait()
.On Windows, the return value is that returned by the system shell after running command. The shell is given by the Windows environment variable
COMSPEC
: it is usually cmd.exe, which returns the exit status of the command run; on systems using a non-native shell, consult your shell documentation.The
subprocess
module provides more powerful facilities for spawning new processes and retrieving their results; using that module is recommended to using this function. See the Replacing Older Functions with the subprocess Module section in thesubprocess
documentation for some helpful recipes.On Unix,
waitstatus_to_exitcode()
can be used to convert the result (exit status) into an exit code. On Windows, the result is directly the exit code.Raises an auditing event
os.system
with argumentcommand
.Availability: Unix, Windows, not WASI, not Android, not iOS.
- os.times()¶
Returns the current global process times. The return value is an object with five attributes:
user
- user timesystem
- system timechildren_user
- user time of all child processeschildren_system
- system time of all child processeselapsed
- elapsed real time since a fixed point in the past
For backwards compatibility, this object also behaves like a five-tuple containing
user
,system
,children_user
,children_system
, andelapsed
in that order.See the Unix manual page times(2) and times(3) manual page on Unix or the GetProcessTimes MSDN on Windows. On Windows, only
user
andsystem
are known; the other attributes are zero.Availability: Unix, Windows.
Changed in version 3.3: Return type changed from a tuple to a tuple-like object with named attributes.
- os.wait()¶
Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced.
If there are no children that could be waited for,
ChildProcessError
is raised.waitstatus_to_exitcode()
can be used to convert the exit status into an exit code.Availability: Unix, not WASI, not Android, not iOS.
See also
The other
wait*()
functions documented below can be used to wait for the completion of a specific child process and have more options.waitpid()
is the only one also available on Windows.
- os.waitid(idtype, id, options, /)¶
Wait for the completion of a child process.
idtype can be
P_PID
,P_PGID
,P_ALL
, or (on Linux)P_PIDFD
. The interpretation of id depends on it; see their individual descriptions.options is an OR combination of flags. At least one of
WEXITED
,WSTOPPED
orWCONTINUED
is required;WNOHANG
andWNOWAIT
are additional optional flags.The return value is an object representing the data contained in the
siginfo_t
structure with the following attributes:si_pid
(process ID)si_uid
(real user ID of the child)si_signo
(alwaysSIGCHLD
)si_status
(the exit status or signal number, depending onsi_code
)si_code
(seeCLD_EXITED
for possible values)
If
WNOHANG
is specified and there are no matching children in the requested state,None
is returned. Otherwise, if there are no matching children that could be waited for,ChildProcessError
is raised.Availability: Unix, not WASI, not Android, not iOS.
Added in version 3.3.
Changed in version 3.13: This function is now available on macOS as well.
- os.waitpid(pid, options, /)¶
The details of this function differ on Unix and Windows.
On Unix: Wait for completion of a child process given by process id pid, and return a tuple containing its process id and exit status indication (encoded as for
wait()
). The semantics of the call are affected by the value of the integer options, which should be0
for normal operation.If pid is greater than
0
,waitpid()
requests status information for that specific process. If pid is0
, the request is for the status of any child in the process group of the current process. If pid is-1
, the request pertains to any child of the current process. If pid is less than-1
, status is requested for any process in the process group-pid
(the absolute value of pid).options is an OR combination of flags. If it contains
WNOHANG
and there are no matching children in the requested state,(0, 0)
is returned. Otherwise, if there are no matching children that could be waited for,ChildProcessError
is raised. Other options that can be used areWUNTRACED
andWCONTINUED
.On Windows: Wait for completion of a process given by process handle pid, and return a tuple containing pid, and its exit status shifted left by 8 bits (shifting makes cross-platform use of the function easier). A pid less than or equal to
0
has no special meaning on Windows, and raises an exception. The value of integer options has no effect. pid can refer to any process whose id is known, not necessarily a child process. Thespawn*
functions called withP_NOWAIT
return suitable process handles.waitstatus_to_exitcode()
can be used to convert the exit status into an exit code.Availability: Unix, Windows, not WASI, not Android, not iOS.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an
InterruptedError
exception (see PEP 475 for the rationale).
- os.wait3(options)¶
Similar to
waitpid()
, except no process id argument is given and a 3-element tuple containing the child’s process id, exit status indication, and resource usage information is returned. Refer toresource.getrusage()
for details on resource usage information. The options argument is the same as that provided towaitpid()
andwait4()
.waitstatus_to_exitcode()
can be used to convert the exit status into an exitcode.Availability: Unix, not WASI, not Android, not iOS.
- os.wait4(pid, options)¶
Similar to
waitpid()
, except a 3-element tuple, containing the child’s process id, exit status indication, and resource usage information is returned. Refer toresource.getrusage()
for details on resource usage information. The arguments towait4()
are the same as those provided towaitpid()
.waitstatus_to_exitcode()
can be used to convert the exit status into an exitcode.Availability: Unix, not WASI, not Android, not iOS.
- os.P_PID¶
- os.P_PGID¶
- os.P_ALL¶
- os.P_PIDFD¶
These are the possible values for idtype in
waitid()
. They affect how id is interpreted:P_PID
- wait for the child whose PID is id.P_PGID
- wait for any child whose progress group ID is id.P_ALL
- wait for any child; id is ignored.P_PIDFD
- wait for the child identified by the file descriptor id (a process file descriptor created withpidfd_open()
).
Availability: Unix, not WASI, not Android, not iOS.
Note
P_PIDFD
is only available on Linux >= 5.4.Added in version 3.3.
Added in version 3.9: The
P_PIDFD
constant.
- os.WCONTINUED¶
This options flag for
waitpid()
,wait3()
,wait4()
, andwaitid()
causes child processes to be reported if they have been continued from a job control stop since they were last reported.Availability: Unix, not WASI, not Android, not iOS.
- os.WEXITED¶
This options flag for
waitid()
causes child processes that have terminated to be reported.The other
wait*
functions always report children that have terminated, so this option is not available for them.Availability: Unix, not WASI, not Android, not iOS.
Added in version 3.3.
- os.WSTOPPED¶
This options flag for
waitid()
causes child processes that have been stopped by the delivery of a signal to be reported.This option is not available for the other
wait*
functions.Availability: Unix, not WASI, not Android, not iOS.
Added in version 3.3.
- os.WUNTRACED¶
This options flag for
waitpid()
,wait3()
, andwait4()
causes child processes to also be reported if they have been stopped but their current state has not been reported since they were stopped.This option is not available for
waitid()
.Availability: Unix, not WASI, not Android, not iOS.
- os.WNOHANG¶
This options flag causes
waitpid()
,wait3()
,wait4()
, andwaitid()
to return right away if no child process status is available immediately.Availability: Unix, not WASI, not Android, not iOS.
- os.WNOWAIT¶
This options flag causes
waitid()
to leave the child in a waitable state, so that a laterwait*()
call can be used to retrieve the child status information again.This option is not available for the other
wait*
functions.Availability: Unix, not WASI, not Android, not iOS.
- os.CLD_EXITED¶
- os.CLD_KILLED¶
- os.CLD_DUMPED¶
- os.CLD_TRAPPED¶
- os.CLD_STOPPED¶
- os.CLD_CONTINUED¶
These are the possible values for
si_code
in the result returned bywaitid()
.Availability: Unix, not WASI, not Android, not iOS.
Added in version 3.3.
Changed in version 3.9: Added
CLD_KILLED
andCLD_STOPPED
values.
- os.waitstatus_to_exitcode(status)¶
Convert a wait status to an exit code.
On Unix:
If the process exited normally (if
WIFEXITED(status)
is true), return the process exit status (returnWEXITSTATUS(status)
): result greater than or equal to 0.If the process was terminated by a signal (if
WIFSIGNALED(status)
is true), return-signum
where signum is the number of the signal that caused the process to terminate (return-WTERMSIG(status)
): result less than 0.Otherwise, raise a
ValueError
.
On Windows, return status shifted right by 8 bits.
On Unix, if the process is being traced or if
waitpid()
was called withWUNTRACED
option, the caller must first check ifWIFSTOPPED(status)
is true. This function must not be called ifWIFSTOPPED(status)
is true.See also
WIFEXITED()
,WEXITSTATUS()
,WIFSIGNALED()
,WTERMSIG()
,WIFSTOPPED()
,WSTOPSIG()
functions.Availability: Unix, Windows, not WASI, not Android, not iOS.
Added in version 3.9.
The following functions take a process status code as returned by
system()
, wait()
, or waitpid()
as a parameter. They may be
used to determine the disposition of a process.
- os.WCOREDUMP(status, /)¶
Return
True
if a core dump was generated for the process, otherwise returnFalse
.This function should be employed only if
WIFSIGNALED()
is true.Availability: Unix, not WASI, not Android, not iOS.
- os.WIFCONTINUED(status)¶
Return
True
if a stopped child has been resumed by delivery ofSIGCONT
(if the process has been continued from a job control stop), otherwise returnFalse
.See
WCONTINUED
option.Availability: Unix, not WASI, not Android, not iOS.
- os.WIFSTOPPED(status)¶
Return
True
if the process was stopped by delivery of a signal, otherwise returnFalse
.WIFSTOPPED()
only returnsTrue
if thewaitpid()
call was done usingWUNTRACED
option or when the process is being traced (see ptrace(2)).Availability: Unix, not WASI, not Android, not iOS.
- os.WIFSIGNALED(status)¶
Return
True
if the process was terminated by a signal, otherwise returnFalse
.Availability: Unix, not WASI, not Android, not iOS.
- os.WIFEXITED(status)¶
Return
True
if the process exited terminated normally, that is, by callingexit()
or_exit()
, or by returning frommain()
; otherwise returnFalse
.Availability: Unix, not WASI, not Android, not iOS.
- os.WEXITSTATUS(status)¶
Return the process exit status.
This function should be employed only if
WIFEXITED()
is true.Availability: Unix, not WASI, not Android, not iOS.
- os.WSTOPSIG(status)¶
Return the signal which caused the process to stop.
This function should be employed only if
WIFSTOPPED()
is true.Availability: Unix, not WASI, not Android, not iOS.
- os.WTERMSIG(status)¶
Return the number of the signal that caused the process to terminate.
This function should be employed only if
WIFSIGNALED()
is true.Availability: Unix, not WASI, not Android, not iOS.
Interface to the scheduler¶
These functions control how a process is allocated CPU time by the operating system. They are only available on some Unix platforms. For more detailed information, consult your Unix manpages.
Added in version 3.3.
The following scheduling policies are exposed if they are supported by the operating system.
- os.SCHED_OTHER¶
The default scheduling policy.
- os.SCHED_BATCH¶
Scheduling policy for CPU-intensive processes that tries to preserve interactivity on the rest of the computer.
- os.SCHED_IDLE¶
Scheduling policy for extremely low priority background tasks.
- os.SCHED_SPORADIC¶
Scheduling policy for sporadic server programs.
- os.SCHED_FIFO¶
A First In First Out scheduling policy.
- os.SCHED_RR¶
A round-robin scheduling policy.
- os.SCHED_RESET_ON_FORK¶
This flag can be OR’ed with any other scheduling policy. When a process with this flag set forks, its child’s scheduling policy and priority are reset to the default.
- class os.sched_param(sched_priority)¶
This class represents tunable scheduling parameters used in
sched_setparam()
,sched_setscheduler()
, andsched_getparam()
. It is immutable.At the moment, there is only one possible parameter:
- sched_priority¶
The scheduling priority for a scheduling policy.
- os.sched_get_priority_min(policy)¶
Get the minimum priority value for policy. policy is one of the scheduling policy constants above.
- os.sched_get_priority_max(policy)¶
Get the maximum priority value for policy. policy is one of the scheduling policy constants above.
- os.sched_setscheduler(pid, policy, param, /)¶
Set the scheduling policy for the process with PID pid. A pid of 0 means the calling process. policy is one of the scheduling policy constants above. param is a
sched_param
instance.
- os.sched_getscheduler(pid, /)¶
Return the scheduling policy for the process with PID pid. A pid of 0 means the calling process. The result is one of the scheduling policy constants above.
- os.sched_setparam(pid, param, /)¶
Set the scheduling parameters for the process with PID pid. A pid of 0 means the calling process. param is a
sched_param
instance.
- os.sched_getparam(pid, /)¶
Return the scheduling parameters as a
sched_param
instance for the process with PID pid. A pid of 0 means the calling process.
- os.sched_rr_get_interval(pid, /)¶
Return the round-robin quantum in seconds for the process with PID pid. A pid of 0 means the calling process.
- os.sched_yield()¶
Voluntarily relinquish the CPU.
- os.sched_setaffinity(pid, mask, /)¶
Restrict the process with PID pid (or the current process if zero) to a set of CPUs. mask is an iterable of integers representing the set of CPUs to which the process should be restricted.
- os.sched_getaffinity(pid, /)¶
Return the set of CPUs the process with PID pid is restricted to.
If pid is zero, return the set of CPUs the calling thread of the current process is restricted to.
See also the
process_cpu_count()
function.
Miscellaneous System Information¶
- os.confstr(name, /)¶
Return string-valued system configuration values. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given as the keys of the
confstr_names
dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.If the configuration value specified by name isn’t defined,
None
is returned.If name is a string and is not known,
ValueError
is raised. If a specific value for name is not supported by the host system, even if it is included inconfstr_names
, anOSError
is raised witherrno.EINVAL
for the error number.Availability: Unix.
- os.confstr_names¶
Dictionary mapping names accepted by
confstr()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
- os.cpu_count()¶
Return the number of logical CPUs in the system. Returns
None
if undetermined.The
process_cpu_count()
function can be used to get the number of logical CPUs usable by the calling thread of the current process.Added in version 3.4.
Changed in version 3.13: If
-X cpu_count
is given orPYTHON_CPU_COUNT
is set,cpu_count()
returns the overridden value n.
- os.getloadavg()¶
Return the number of processes in the system run queue averaged over the last 1, 5, and 15 minutes or raises
OSError
if the load average was unobtainable.Availability: Unix.
- os.process_cpu_count()¶
Get the number of logical CPUs usable by the calling thread of the current process. Returns
None
if undetermined. It can be less thancpu_count()
depending on the CPU affinity.The
cpu_count()
function can be used to get the number of logical CPUs in the system.If
-X cpu_count
is given orPYTHON_CPU_COUNT
is set,process_cpu_count()
returns the overridden value n.See also the
sched_getaffinity()
function.Added in version 3.13.
- os.sysconf(name, /)¶
Return integer-valued system configuration values. If the configuration value specified by name isn’t defined,
-1
is returned. The comments regarding the name parameter forconfstr()
apply here as well; the dictionary that provides information on the known names is given bysysconf_names
.Availability: Unix.
- os.sysconf_names¶
Dictionary mapping names accepted by
sysconf()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
Changed in version 3.11: Add
'SC_MINSIGSTKSZ'
name.
The following data values are used to support path manipulation operations. These are defined for all platforms.
Higher-level operations on pathnames are defined in the os.path
module.
- os.curdir¶
The constant string used by the operating system to refer to the current directory. This is
'.'
for Windows and POSIX. Also available viaos.path
.
- os.pardir¶
The constant string used by the operating system to refer to the parent directory. This is
'..'
for Windows and POSIX. Also available viaos.path
.
- os.sep¶
The character used by the operating system to separate pathname components. This is
'/'
for POSIX and'\\'
for Windows. Note that knowing this is not sufficient to be able to parse or concatenate pathnames — useos.path.split()
andos.path.join()
— but it is occasionally useful. Also available viaos.path
.
- os.altsep¶
An alternative character used by the operating system to separate pathname components, or
None
if only one separator character exists. This is set to'/'
on Windows systems wheresep
is a backslash. Also available viaos.path
.
- os.extsep¶
The character which separates the base filename from the extension; for example, the
'.'
inos.py
. Also available viaos.path
.
- os.pathsep¶
The character conventionally used by the operating system to separate search path components (as in
PATH
), such as':'
for POSIX or';'
for Windows. Also available viaos.path
.
- os.defpath¶
The default search path used by
exec*p*
andspawn*p*
if the environment doesn’t have a'PATH'
key. Also available viaos.path
.
- os.linesep¶
The string used to separate (or, rather, terminate) lines on the current platform. This may be a single character, such as
'\n'
for POSIX, or multiple characters, for example,'\r\n'
for Windows. Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single'\n'
instead, on all platforms.
- os.devnull¶
The file path of the null device. For example:
'/dev/null'
for POSIX,'nul'
for Windows. Also available viaos.path
.
- os.RTLD_LAZY¶
- os.RTLD_NOW¶
- os.RTLD_GLOBAL¶
- os.RTLD_LOCAL¶
- os.RTLD_NODELETE¶
- os.RTLD_NOLOAD¶
- os.RTLD_DEEPBIND¶
Flags for use with the
setdlopenflags()
andgetdlopenflags()
functions. See the Unix manual page dlopen(3) for what the different flags mean.Added in version 3.3.
Random numbers¶
- os.getrandom(size, flags=0)¶
Get up to size random bytes. The function can return less bytes than requested.
These bytes can be used to seed user-space random number generators or for cryptographic purposes.
getrandom()
relies on entropy gathered from device drivers and other sources of environmental noise. Unnecessarily reading large quantities of data will have a negative impact on other users of the/dev/random
and/dev/urandom
devices.The flags argument is a bit mask that can contain zero or more of the following values ORed together:
os.GRND_RANDOM
andGRND_NONBLOCK
.See also the Linux getrandom() manual page.
Availability: Linux >= 3.17.
Added in version 3.6.
- os.urandom(size, /)¶
Return a bytestring of size random bytes suitable for cryptographic use.
This function returns random bytes from an OS-specific randomness source. The returned data should be unpredictable enough for cryptographic applications, though its exact quality depends on the OS implementation.
On Linux, if the
getrandom()
syscall is available, it is used in blocking mode: block until the system urandom entropy pool is initialized (128 bits of entropy are collected by the kernel). See the PEP 524 for the rationale. On Linux, thegetrandom()
function can be used to get random bytes in non-blocking mode (using theGRND_NONBLOCK
flag) or to poll until the system urandom entropy pool is initialized.On a Unix-like system, random bytes are read from the
/dev/urandom
device. If the/dev/urandom
device is not available or not readable, theNotImplementedError
exception is raised.On Windows, it will use
BCryptGenRandom()
.See also
The
secrets
module provides higher level functions. For an easy-to-use interface to the random number generator provided by your platform, please seerandom.SystemRandom
.Changed in version 3.5: On Linux 3.17 and newer, the
getrandom()
syscall is now used when available. On OpenBSD 5.6 and newer, the Cgetentropy()
function is now used. These functions avoid the usage of an internal file descriptor.Changed in version 3.5.2: On Linux, if the
getrandom()
syscall blocks (the urandom entropy pool is not initialized yet), fall back on reading/dev/urandom
.Changed in version 3.6: On Linux,
getrandom()
is now used in blocking mode to increase the security.Changed in version 3.11: On Windows,
BCryptGenRandom()
is used instead ofCryptGenRandom()
which is deprecated.
- os.GRND_NONBLOCK¶
By default, when reading from
/dev/random
,getrandom()
blocks if no random bytes are available, and when reading from/dev/urandom
, it blocks if the entropy pool has not yet been initialized.If the
GRND_NONBLOCK
flag is set, thengetrandom()
does not block in these cases, but instead immediately raisesBlockingIOError
.Added in version 3.6.
- os.GRND_RANDOM¶
If this bit is set, then random bytes are drawn from the
/dev/random
pool instead of the/dev/urandom
pool.Added in version 3.6.