"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.

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.

exception os.error

   An alias for the built-in "OSError" exception.

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
=================

New 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", and "sys.stderr" all use UTF-8 as their
  text encoding, with the "surrogateescape" error handler being
  enabled for "sys.stdin" and "sys.stdout" ("sys.stderr" continues to
  use "backslashreplace" 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()" and "os.fsencode()" use the UTF-8 encoding.

* "open()", "io.open()", and "codecs.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*.


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.

os.environ

   A *mapping* object representing the string environment. For
   example, "environ['HOME']" is the pathname of your home directory
   (on some platforms), and is equivalent to "getenv("HOME")" in C.

   This mapping is captured the first time the "os" module is
   imported, typically during Python startup as part of processing
   "site.py".  Changes to the environment made after this time are not
   reflected in "os.environ", except for changes made by modifying
   "os.environ" directly.

   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. Use "environb" if you would like
   to use a different encoding.

   Note:

     Calling "putenv()" directly does not change "os.environ", so it's
     better to modify "os.environ".

   Note:

     On some platforms, including FreeBSD and Mac OS X, setting
     "environ" may cause memory leaks.  Refer to the system
     documentation for "putenv()".

   You can delete items in this mapping to unset environment
   variables. "unsetenv()" will be called automatically when an item
   is deleted from "os.environ", and when one of the "pop()" or
   "clear()" methods is called.

   Changed in version 3.9: Updated to support **PEP 584**'s merge
   ("|") and update ("|=") operators.

os.environb

   Bytes version of "environ": a *mapping* object representing the
   environment as byte strings. "environ" and "environb" are
   synchronized (modify "environb" updates "environ", and vice versa).

   "environb" is only available if "supports_bytes_environ" is "True".

   New 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.

   New 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.

   New 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" or "bytes" is passed in, it is returned unchanged.
   Otherwise "__fspath__()" is called and its value is returned as
   long as it is a "str" or "bytes" object. In all other cases,
   "TypeError" is raised.

   New in version 3.6.

class os.PathLike

   An *abstract base class* for objects representing a file system
   path, e.g. "pathlib.PurePath".

   New in version 3.6.

   abstractmethod __fspath__()

      Return the file system path representation of the object.

      The method should only return a "str" or "bytes" object, with
      the preference being for "str".

os.getenv(key, default=None)

   Return the value of the environment variable *key* if it exists, or
   *default* if it doesn't. *key*, *default* and the result are str.

   On Unix, keys and values are decoded with
   "sys.getfilesystemencoding()" and "'surrogateescape'" error
   handler. Use "os.getenvb()" if you would like to use a different
   encoding.

   Availability: most flavors of Unix, Windows.

os.getenvb(key, default=None)

   Return the value of the environment variable *key* if it exists, or
   *default* if it doesn't. *key*, *default* and the result are bytes.

   "getenvb()" is only available if "supports_bytes_environ" is
   "True".

   Availability: most flavors of Unix.

   New 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.

   New 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.

os.geteuid()

   Return the current process's effective user id.

   Availability: Unix.

os.getgid()

   Return the real group id of the current process.

   Availability: Unix.

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*.

   Availability: Unix.

   New in version 3.3.

os.getgroups()

   Return list of supplemental group ids associated with the current
   process.

   Availability: Unix.

   Note:

     On Mac OS X, "getgroups()" behavior differs somewhat from other
     Unix platforms. If the Python interpreter was built with a
     deployment target of "10.5" 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 to
     "setgroups()" if suitably privileged. If built with a deployment
     target greater than "10.5", "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 to
     "setgroups()", and its length is not limited to 16.  The
     deployment target value, "MACOSX_DEPLOYMENT_TARGET", can be
     obtained with "sysconfig.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
   variables "LOGNAME" or "USERNAME" to find out who the user is, and
   falls back to "pwd.getpwuid(os.getuid())[0]" to get the login name
   of the current real user id.

   Availability: Unix, Windows.

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.

os.getpgrp()

   Return the id of the current process group.

   Availability: Unix.

os.getpid()

   Return the current process id.

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.

   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", or "PRIO_USER", and *who* is
   interpreted relative to *which* (a process identifier for
   "PRIO_PROCESS", process group identifier for "PRIO_PGRP", and a
   user ID for "PRIO_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.

   New in version 3.3.

os.PRIO_PROCESS
os.PRIO_PGRP
os.PRIO_USER

   Parameters for the "getpriority()" and "setpriority()" functions.

   Availability: Unix.

   New in version 3.3.

os.getresuid()

   Return a tuple (ruid, euid, suid) denoting the current process's
   real, effective, and saved user ids.

   Availability: Unix.

   New 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.

   New in version 3.2.

os.getuid()

   Return the current process's real user id.

   Availability: Unix.

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.

   New 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()" or "fork()" and "execv()".

   Assignments to items in "os.environ" are automatically translated
   into corresponding calls to "putenv()"; however, calls to
   "putenv()" don't update "os.environ", so it is actually preferable
   to assign to items of "os.environ".

   Note:

     On some platforms, including FreeBSD and Mac OS X, setting
     "environ" may cause memory leaks. Refer to the system
     documentation for "putenv()".

   Raises an auditing event "os.putenv" with arguments "key", "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.

os.seteuid(euid)

   Set the current process's effective user id.

   Availability: Unix.

os.setgid(gid)

   Set the current process' group id.

   Availability: Unix.

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.

   Note:

     On Mac OS X, 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.setpgrp()

   Call the system call "setpgrp()" or "setpgrp(0, 0)" depending on
   which version is implemented (if any).  See the Unix manual for the
   semantics.

   Availability: Unix.

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.

os.setpriority(which, who, priority)

   Set program scheduling priority. The value *which* is one of
   "PRIO_PROCESS", "PRIO_PGRP", or "PRIO_USER", and *who* is
   interpreted relative to *which* (a process identifier for
   "PRIO_PROCESS", process group identifier for "PRIO_PGRP", and a
   user ID for "PRIO_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.

   New in version 3.3.

os.setregid(rgid, egid)

   Set the current process's real and effective group ids.

   Availability: Unix.

os.setresgid(rgid, egid, sgid)

   Set the current process's real, effective, and saved group ids.

   Availability: Unix.

   New in version 3.2.

os.setresuid(ruid, euid, suid)

   Set the current process's real, effective, and saved user ids.

   Availability: Unix.

   New in version 3.2.

os.setreuid(ruid, euid)

   Set the current process's real and effective user ids.

   Availability: Unix.

os.getsid(pid)

   Call the system call "getsid()".  See the Unix manual for the
   semantics.

   Availability: Unix.

os.setsid()

   Call the system call "setsid()".  See the Unix manual for the
   semantics.

   Availability: Unix.

os.setuid(uid)

   Set the current process's user id.

   Availability: Unix.

os.strerror(code)

   Return the error message corresponding to the error code in *code*.
   On platforms where "strerror()" returns "NULL" 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).

   New in version 3.2.

os.umask(mask)

   Set the current numeric umask and return the previous umask.

os.uname()

   Returns information identifying the current operating system. The
   return value is an object with five attributes:

   * "sysname" - operating system name

   * "nodename" - name of machine on network (implementation-defined)

   * "release" - operating system release

   * "version" - operating system version

   * "machine" - hardware identifier

   For backwards compatibility, this object is also iterable, behaving
   like a five-tuple containing "sysname", "nodename", "release",
   "version", and "machine" in that order.

   Some systems truncate "nodename" to 8 characters or to the leading
   component; a better way to get the hostname is
   "socket.gethostname()"  or even
   "socket.gethostbyaddr(socket.gethostname())".

   Availability: recent flavors of 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()" or "fork()" and "execv()".

   Deletion of items in "os.environ" is automatically translated into
   a corresponding call to "unsetenv()"; however, calls to
   "unsetenv()" don't update "os.environ", so it is actually
   preferable to delete items of "os.environ".

   Raises an auditing event "os.unsetenv" with argument "key".

   Changed in version 3.9: The function is now always available and is
   also available on Windows.


File Object Creation
====================

These functions create new *file objects*.  (See also "open()" for
opening file descriptors.)

os.fdopen(fd, *args, **kwargs)

   Return an open file object connected to the file descriptor *fd*.
   This is an alias of the "open()" built-in function and accepts the
   same arguments. The only difference is that the first argument of
   "fdopen()" must always be an integer.


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*.

   Note:

     This function is intended for low-level I/O and must be applied
     to a file descriptor as returned by "os.open()" or "pipe()".  To
     close a "file object" returned by the built-in function "open()"
     or by "popen()" or "fdopen()", use its "close()" method.

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*. The files pointed
   by *src* and *dst* must reside in the same filesystem, otherwise an
   "OSError" is raised with "errno" set to "errno.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.

   The return value is the amount of bytes copied. This could be less
   than the amount requested.

   Availability: Linux kernel >= 4.5 or glibc >= 2.27.

   New 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.

   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".

   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 to "os.chmod(fd, mode)".

   Raises an auditing event "os.chmod" with arguments "path", "mode",
   "dir_fd".

   Availability: Unix.

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 to
   "os.chown(fd, uid, gid)".

   Raises an auditing event "os.chown" with arguments "path", "uid",
   "gid", "dir_fd".

   Availability: Unix.

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 in "pathconf_names", an "OSError" is raised
   with "errno.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 to "os.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 do "os.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 arguments "fd",
   "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 the
   "O_NONBLOCK" flag is set, "True" if the flag is cleared.

   See also "set_blocking()" and "socket.socket.setblocking()".

   Availability: Unix.

   New in version 3.5.

os.isatty(fd)

   Return "True" if the file descriptor *fd* is open and connected to
   a tty(-like) device, else "False".

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" or "F_TEST". *len* specifies
   the section of the file to lock.

   Raises an auditing event "os.lockf" with arguments "fd", "cmd",
   "len".

   Availability: Unix.

   New 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.

   New in version 3.3.

os.lseek(fd, pos, how)

   Set the current position of file descriptor *fd* to position *pos*,
   modified by *how*: "SEEK_SET" or "0" to set the position relative
   to the beginning of the file; "SEEK_CUR" or "1" to set it relative
   to the current position; "SEEK_END" or "2" to set it relative to
   the end of the file. Return the new cursor position in bytes,
   starting from the beginning.

os.SEEK_SET
os.SEEK_CUR
os.SEEK_END

   Parameters to the "lseek()" function. Their values are 0, 1, and 2,
   respectively.

   New in version 3.3: Some operating systems could support additional
   values, like "os.SEEK_HOLE" or "os.SEEK_DATA".

os.open(path, flags, mode=511, *, 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" and "O_WRONLY") are
   defined in the "os" module.  In particular, on Windows adding
   "O_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 arguments "path", "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*
     with "read()" and "write()" methods (and many more).  To wrap a
     file descriptor in a file object, use "fdopen()".

   New in version 3.3: The *dir_fd* argument.

   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"
   and "O_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.

   Changed in version 3.4: Add "O_PATH" on systems that support it.
   Add "O_TMPFILE", only available on Linux Kernel 3.11   or newer.

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 the "pty" module.

   Availability: some flavors of Unix.

   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: some flavors of Unix.

   New 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.

   New 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" or "POSIX_FADV_DONTNEED".

   Availability: Unix.

   New 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.

   New 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.

   New in version 3.3.

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:

   * "RWF_HIPRI"

   * "RWF_NOWAIT"

   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()" and "os.pread()".

   Availability: Linux 2.6.30 and newer, FreeBSD 6.0 and newer,
   OpenBSD 2.7 and newer, AIX 7.1 and newer. Using flags requires
   Linux 4.6 or newer.

   New 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 to "errno.EAGAIN".

   Availability: Linux 4.14 and newer.

   New 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 and newer.

   New in version 3.7.

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.

   New in version 3.3.

os.pwritev(fd, buffers, offset, flags=0)

   Write the *buffers* contents to file descriptor *fd* at a 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:

   * "RWF_DSYNC"

   * "RWF_SYNC"

   * "RWF_APPEND"

   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()" and "os.pwrite()".

   Availability: Linux 2.6.30 and newer, FreeBSD 6.0 and newer,
   OpenBSD 2.7 and newer, AIX 7.1 and newer. Using flags requires
   Linux 4.7 or newer.

   New 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 and newer.

   New 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 and newer.

   New in version 3.7.

os.RWF_APPEND

   Provide a per-write equivalent of the "O_APPEND" "os.open()" flag.
   This flag is meaningful only for "os.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 and newer.

   New 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()" or "pipe()".  To
     read a "file object" returned by the built-in function "open()"
     or by "popen()" or "fdopen()", or "sys.stdin", use its "read()"
     or "readline()" 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 Mac OS X 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 Mac OS X 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.

   Note:

     For a higher-level wrapper of "sendfile()", see
     "socket.socket.sendfile()".

   New in version 3.3.

   Changed in version 3.9: Parameters *out* and *in* was renamed to
   *out_fd* and *in_fd*.

os.set_blocking(fd, blocking)

   Set the blocking mode of the specified file descriptor. Set the
   "O_NONBLOCK" flag if blocking is "False", clear the flag otherwise.

   See also "get_blocking()" and "socket.socket.setblocking()".

   Availability: Unix.

   New in version 3.5.

os.SF_NODISKIO
os.SF_MNOWAIT
os.SF_SYNC

   Parameters to the "sendfile()" function, if the implementation
   supports them.

   Availability: Unix.

   New in version 3.3.

os.splice(src, dst, count, offset_src=None, offset_dst=None)

   Transfer *count* bytes from file descriptor *src*, starting from
   offset *offset_src*, to file descriptor *dst*, starting from offset
   *offset_dst*. 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 be "None". The files
   pointed by *src* and *dst* must reside in the same filesystem,
   otherwise an "OSError" is raised with "errno" set to "errno.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.

   Availability: Linux kernel >= 2.6.17 and glibc >= 2.5

   New in version 3.10.

os.SPLICE_F_MOVE
os.SPLICE_F_NONBLOCK
os.SPLICE_F_MORE

   New 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.

   New 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.

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.

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.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()" or "pipe()".  To
     write a "file object" returned by the built-in function "open()"
     or by "popen()" or "fdopen()", or "sys.stdout" or "sys.stderr",
     use its "write()" 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.

   New in version 3.3.


Querying the size of a terminal
-------------------------------

New in version 3.3.

os.get_terminal_size(fd=STDOUT_FILENO)

   Return the size of the terminal window as "(columns, lines)", tuple
   of type "terminal_size".

   The optional argument "fd" (default "STDOUT_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.

class os.terminal_size

   A subclass of tuple, holding "(columns, lines)" of the terminal
   window size.

   columns

      Width of the terminal window in characters.

   lines

      Height of the terminal window in characters.


Inheritance of File Descriptors
-------------------------------

New 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".

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 with
  "f" (e.g. call "fchdir" instead of "chdir").)

  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 a "NotImplementedError".

  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 an "at" suffix and possibly prefixed with "f" (e.g.
  call "faccessat" instead of "access").

  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 a "NotImplementedError".

* **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
  the "l..." 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 a "NotImplementedError".

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 of "R_OK", "W_OK", and "X_OK" to test permissions.  Return
   "True" 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 using
   "os.supports_effective_ids".  If it is unavailable, using it will
   raise a "NotImplementedError".

   Note:

     Using "access()" to check if a user is authorized to e.g. open a
     file before actually doing so using "open()" 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 as
   "FileNotFoundError", "PermissionError", and "NotADirectoryError".

   Raises an auditing event "os.chdir" with argument "path".

   New 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):

   * "stat.UF_NODUMP"

   * "stat.UF_IMMUTABLE"

   * "stat.UF_APPEND"

   * "stat.UF_OPAQUE"

   * "stat.UF_NOUNLINK"

   * "stat.UF_COMPRESSED"

   * "stat.UF_HIDDEN"

   * "stat.SF_ARCHIVED"

   * "stat.SF_IMMUTABLE"

   * "stat.SF_APPEND"

   * "stat.SF_NOUNLINK"

   * "stat.SF_SNAPSHOT"

   This function can support not following symlinks.

   Raises an auditing event "os.chflags" with arguments "path",
   "flags".

   Availability: Unix.

   New in version 3.3: The *follow_symlinks* argument.

   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:

   * "stat.S_ISUID"

   * "stat.S_ISGID"

   * "stat.S_ENFMT"

   * "stat.S_ISVTX"

   * "stat.S_IREAD"

   * "stat.S_IWRITE"

   * "stat.S_IEXEC"

   * "stat.S_IRWXU"

   * "stat.S_IRUSR"

   * "stat.S_IWUSR"

   * "stat.S_IXUSR"

   * "stat.S_IRWXG"

   * "stat.S_IRGRP"

   * "stat.S_IWGRP"

   * "stat.S_IXGRP"

   * "stat.S_IRWXO"

   * "stat.S_IROTH"

   * "stat.S_IWOTH"

   * "stat.S_IXOTH"

   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 the "stat.S_IWRITE" and
     "stat.S_IREAD" constants or a corresponding integer value).  All
     other bits are ignored.

   Raises an auditing event "os.chmod" with arguments "path", "mode",
   "dir_fd".

   New 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*.

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 arguments "path", "uid",
   "gid", "dir_fd".

   Availability: Unix.

   New 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.

   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 argument "path".

   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 to "os.chflags(path, flags, follow_symlinks=False)".

   Raises an auditing event "os.chflags" with arguments "path",
   "flags".

   Availability: Unix.

   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 to "os.chmod(path, mode,
   follow_symlinks=False)".

   Raises an auditing event "os.chmod" with arguments "path", "mode",
   "dir_fd".

   Availability: Unix.

   Changed in version 3.6: Accepts a *path-like object*.

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 arguments "path", "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 arguments "src", "dst",
   "src_dir_fd", "dst_dir_fd".

   Availability: Unix, Windows.

   Changed in version 3.2: Added Windows support.

   New in version 3.3: Added the *src_dir_fd*, *dst_dir_fd*, and
   *follow_symlinks* arguments.

   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 the "PathLike" interface), the
   filenames returned will also be of type "bytes"; in all other
   circumstances, they will be of type "str".

   This function can also support specifying a file descriptor; the
   file descriptor must refer to a directory.

   Raises an auditing event "os.listdir" with argument "path".

   Note:

     To encode "str" filenames to "bytes", use "fsencode()".

   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.

   New 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.lstat(path, *, dir_fd=None)

   Perform the equivalent of an "lstat()" system call on the given
   path. Similar to "stat()", but does not follow symbolic links.
   Return a "stat_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=511, *, dir_fd=None)

   Create a directory named *path* with numeric mode *mode*.

   If the directory already exists, "FileExistsError" 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.

   This function can also support paths relative to directory
   descriptors.

   It is also possible to create temporary directories; see the
   "tempfile" module's "tempfile.mkdtemp()" function.

   Raises an auditing event "os.mkdir" with arguments "path", "mode",
   "dir_fd".

   New in version 3.3: The *dir_fd* argument.

   Changed in version 3.6: Accepts a *path-like object*.

os.makedirs(name, mode=511, 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 invoking "makedirs()".
   The file permission bits of existing parent directories are not
   changed.

   If *exist_ok* is "False" (the default), an "FileExistsError" is
   raised if the target directory already exists.

   Note:

     "makedirs()" will become confused if the path elements to create
     include "pardir" (eg. ".." on UNIX systems).

   This function handles UNC paths correctly.

   Raises an auditing event "os.mkdir" with arguments "path", "mode",
   "dir_fd".

   New in version 3.2: 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=438, *, 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 that "mkfifo()" doesn't open
   the FIFO --- it just creates the rendezvous point.

   Availability: Unix.

   New in version 3.3: The *dir_fd* argument.

   Changed in version 3.6: Accepts a *path-like object*.

os.mknod(path, mode=384, 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", and "stat.S_IFIFO"
   (those constants are available in "stat").  For "stat.S_IFCHR" and
   "stat.S_IFBLK", *device* defines the newly created device special
   file (probably using "os.makedev()"), otherwise it is ignored.

   This function can also support paths relative to directory
   descriptors.

   Availability: Unix.

   New in version 3.3: The *dir_fd* argument.

   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" or "st_rdev" field from "stat").

os.minor(device)

   Extract the device minor number from a raw device number (usually
   the "st_dev" or "st_rdev" field from "stat").

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 in "pathconf_names", an "OSError" is raised
   with "errno.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()" and "fpathconf()"
   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.

   New in version 3.3: The *dir_fd* argument.

   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.

   Changed in version 3.8: 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
   "IsADirectoryError" is raised.  Use "rmdir()" to remove
   directories. If the file does not exist, a "FileNotFoundError" 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 arguments "path",
   "dir_fd".

   New in version 3.3: The *dir_fd* argument.

   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. Raises "OSError" if the leaf directory could not be
   successfully removed.

   Raises an auditing event "os.remove" with arguments "path",
   "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.

   On Unix, if *src* is a file and *dst* is a directory or vice-versa,
   an "IsADirectoryError" or a "NotADirectoryError" will be raised
   respectively.  If both are directories and *dst* is empty, *dst*
   will be silently replaced.  If *dst* is a non-empty directory, an
   "OSError" is raised. If both are files, *dst* it 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 arguments "src", "dst",
   "src_dir_fd", "dst_dir_fd".

   New in version 3.3: The *src_dir_fd* and *dst_dir_fd* arguments.

   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 using "removedirs()".

   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 arguments "src", "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
   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 arguments "src", "dst",
   "src_dir_fd", "dst_dir_fd".

   New 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, an "FileNotFoundError" or an "OSError" 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 arguments "path",
   "dir_fd".

   New in version 3.3: 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 of "listdir()" can significantly increase
   the performance of code that also needs file type or file attribute
   information, because "os.DirEntry" objects expose this information
   if the operating system provides it when scanning a directory. All
   "os.DirEntry" methods may perform a system call, but "is_dir()" and
   "is_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 the "PathLike" interface), the type
   of the "name" and "path" attributes of each "os.DirEntry" will be
   "bytes"; in all other circumstances, they will be of type "str".

   This function can also support specifying a file descriptor; the
   file descriptor must refer to a directory.

   Raises an auditing event "os.scandir" with argument "path".

   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.

      New 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 "'.'". The "entry.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.

   New in version 3.5.

   New in version 3.6: Added support for the *context manager*
   protocol and the "close()" method.  If a "scandir()" iterator is
   neither exhausted nor explicitly closed a "ResourceWarning" 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 a "stat()" or
   "lstat()" system call is made, the "os.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 calling "scandir()", call
   "os.stat(entry.path)" to fetch up-to-date information.

   Because the "os.DirEntry" methods can make operating system calls,
   they may also raise "OSError". If you need very fine-grained
   control over errors, you can catch "OSError" when calling one of
   the "os.DirEntry" methods and handle as appropriate.

   To be directly usable as a *path-like object*, "os.DirEntry"
   implements the "PathLike" 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 be "bytes" if the "scandir()" *path*
      argument is of type "bytes" and "str" otherwise.  Use
      "fsdecode()" to decode byte filenames.

   path

      The entry's full path name: equivalent to
      "os.path.join(scandir_path, entry.name)" where *scandir_path* is
      the "scandir()" *path* argument.  The path is only absolute if
      the "scandir()" *path* argument was absolute.  If the
      "scandir()" *path* argument was a file descriptor, the "path"
      attribute is the same as the "name" attribute.

      The "path" attribute will be "bytes" if the "scandir()" *path*
      argument is of type "bytes" and "str" otherwise.  Use
      "fsdecode()" to decode byte filenames.

   inode()

      Return the inode number of the entry.

      The result is cached on the "os.DirEntry" object. Use
      "os.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; return "False" if the entry is or
      points to any other kind of file, or if it doesn't exist
      anymore.

      If *follow_symlinks* is "False", return "True" only if this
      entry is a directory (without following symlinks); return
      "False" 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_symlinks* "True" and "False". Call
      "os.stat()" along with "stat.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* is
      "False".

      This method can raise "OSError", such as "PermissionError", but
      "FileNotFoundError" 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; return "False" 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", return "True" only if this
      entry is a file (without following symlinks); return "False" 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 per "is_dir()".

   is_symlink()

      Return "True" if this entry is a symbolic link (even if broken);
      return "False" 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. Call
      "os.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 as "PermissionError", but
      "FileNotFoundError" is caught and not raised.

   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
      the "follow_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" and "st_nlink" attributes of
      the "stat_result" are always set to zero. Call "os.stat()" to
      get these attributes.

      The result is cached on the "os.DirEntry" object, with a
      separate cache for *follow_symlinks* "True" and "False". Call
      "os.stat()" to fetch up-to-date information.

   Note that there is a nice correspondence between several attributes
   and methods of "os.DirEntry" and of "pathlib.Path".  In particular,
   the "name" attribute has the same meaning, as do the "is_dir()",
   "is_file()", "is_symlink()" and "stat()" methods.

   New in version 3.5.

   Changed in version 3.6: Added support for the "PathLike" interface.
   Added support for "bytes" paths on Windows.

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 the "PathLike" interface -- or as an open file descriptor.
   Return a "stat_result" object.

   This function normally follows symlinks; to stat a symlink add the
   argument "follow_symlinks=False", or use "lstat()".

   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 the "os.path.realpath()" function
   to resolve the path name as far as possible and call "lstat()" 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

   See also: "fstat()" and "lstat()" functions.

   New in version 3.3: Added the *dir_fd* and *follow_symlinks*
   arguments, 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 if "follow_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 of "os.stat()",
   "os.fstat()" and "os.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

      Platform dependent:

      * the time of most recent metadata change on Unix,

      * the time of creation on Windows, expressed in seconds.

   st_atime_ns

      Time of most recent access expressed in nanoseconds as an
      integer.

   st_mtime_ns

      Time of most recent content modification expressed in
      nanoseconds as an integer.

   st_ctime_ns

      Platform dependent:

      * the time of most recent metadata change on Unix,

      * the time of creation on Windows, expressed in nanoseconds as
        an integer.

   Note:

     The exact meaning and resolution of the "st_atime", "st_mtime",
     and "st_ctime" attributes depend on the operating system and the
     file system. For example, on Windows systems using the FAT or
     FAT32 file systems, "st_mtime" has 2-second resolution, and
     "st_atime" has only 1-day resolution.  See your operating system
     documentation for details.Similarly, although "st_atime_ns",
     "st_mtime_ns", and "st_ctime_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 store "st_atime", "st_mtime", and "st_ctime"
     cannot preserve all of it, and as such will be slightly inexact.
     If you need the exact timestamps you should always use
     "st_atime_ns", "st_mtime_ns", and "st_ctime_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.

   st_birthtime

      Time of file creation.

   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 Mac OS 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 the
      "BY_HANDLE_FILE_INFORMATION" structure returned by
      "GetFileInformationByHandle()". See the "FILE_ATTRIBUTE_*"
      constants in the "stat" module.

   st_reparse_tag

      When "st_file_attributes" has the "FILE_ATTRIBUTE_REPARSE_POINT"
      set, this field contains the tag identifying the type of reparse
      point. See the "IO_REPARSE_TAG_*" constants in the "stat"
      module.

   The standard module "stat" defines functions and constants that are
   useful for extracting information from a "stat" 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 the "stat" structure, in the
   order "st_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, accessing "stat_result" as a tuple
   always returns integers.

   New in version 3.3: Added the "st_atime_ns", "st_mtime_ns", and
   "st_ctime_ns" members.

   New in version 3.5: Added the "st_file_attributes" member on
   Windows.

   Changed in version 3.5: Windows now returns the file index as
   "st_ino" when available.

   New in version 3.7: Added the "st_fstype" member to
   Solaris/derivatives.

   New 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 as "S_IFCHR", "S_IFIFO" or "S_IFBLK" as
   appropriate.

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 the "statvfs"
   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: if "ST_RDONLY" is set, the filesystem is mounted read-
   only, and if "ST_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" and "ST_NOSUID" constants
   were added.

   New 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", and "ST_RELATIME"
   constants were added.

   Changed in version 3.6: Accepts a *path-like object*.

   New in version 3.7: Added "f_fsid".

os.supports_dir_fd

   A "set" object indicating which functions in the "os" 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. (Specifying "None" 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 on
   "supports_dir_fd". As an example, this expression evaluates to
   "True" if "os.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.

   New in version 3.3.

os.supports_effective_ids

   A "set" object indicating whether "os.access()" permits specifying
   "True" for its *effective_ids* parameter on the local platform.
   (Specifying "False" for *effective_ids* is always supported on all
   platforms.)  If the local platform supports it, the collection will
   contain "os.access()"; otherwise it will be empty.

   This expression evaluates to "True" if "os.access()" supports
   "effective_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.

   New in version 3.3.

os.supports_fd

   A "set" object indicating which functions in the "os" 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 on "supports_fd". As an example, this expression evaluates
   to "True" if "os.chdir()" accepts open file descriptors for *path*
   on your local platform:

      os.chdir in os.supports_fd

   New in version 3.3.

os.supports_follow_symlinks

   A "set" object indicating which functions in the "os" module accept
   "False" 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.
   (Specifying "True" for *follow_symlinks* is always supported on all
   platforms.)

   To check whether a particular function accepts "False" for its
   *follow_symlinks* parameter, use the "in" operator on
   "supports_follow_symlinks".  As an example, this expression
   evaluates to "True" if you may specify "follow_symlinks=False" when
   calling "os.stat()" on the local platform:

      os.stat in os.supports_follow_symlinks

   New 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 arguments "src", "dst",
   "dir_fd".

   Availability: Unix, Windows.

   Changed in version 3.2: Added support for Windows 6.0 (Vista)
   symbolic links.

   New in version 3.3: Added the *dir_fd* argument, 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.

   New 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 arguments "path",
   "length".

   Availability: Unix, Windows.

   New 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()"; the "unlink" name is its traditional Unix
   name.  Please see the documentation for "remove()" for further
   information.

   Raises an auditing event "os.remove" with arguments "path",
   "dir_fd".

   New in version 3.3: 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 specifying "ns=(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; see
   "stat()". The best way to preserve exact times is to use the
   *st_atime_ns* and *st_mtime_ns* fields from the "os.stat()" result
   object with the *ns* parameter to *utime*.

   This function can support specifying a file descriptor, paths
   relative to directory descriptors and not following symlinks.

   Raises an auditing event "os.utime" with arguments "path", "times",
   "ns", "dir_fd".

   New 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* (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*, do
   "os.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* is "False", 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 using "del" or slice assignment), and "walk()"
   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 inform "walk()" about directories the
   caller creates or renames before it resumes "walk()" again.
   Modifying *dirnames* when *topdown* is "False" 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, an "OSError" 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 the
   "filename" attribute of the exception object.

   By default, "walk()" will not walk down into symbolic links that
   resolve to directories. Set *followlinks* to "True" 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))

   Raises an auditing event "os.walk" with arguments "top", "topdown",
   "onerror", "followlinks".

   Changed in version 3.5: This function now calls "os.scandir()"
   instead of "os.listdir()", making it faster by reducing the number
   of calls to "os.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 supports "dir_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*
   is "False".

   Note:

     Since "fwalk()" yields file descriptors, those are only valid
     until the next iteration step, so you should duplicate them (e.g.
     with "dup()") 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 arguments "top",
   "topdown", "onerror", "follow_symlinks", "dir_fd".

   Availability: Unix.

   New 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
   with "memfd:" 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 or newer with glibc 2.27 or newer.

   New 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 or newer with glibc 2.27 or newer.  The
   "MFD_HUGE*" flags are only available since Linux 4.14.

   New in version 3.8.

os.eventfd(initval[, flags=os.EFD_CLOEXEC])

   Create and return an event file descriptor. The file descriptors
   supports raw "read()" and "write()" 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 an 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
   2^64-2.

   *flags* can be constructed from "EFD_CLOEXEC", "EFD_NONBLOCK", and
   "EFD_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
   2^64-2.

   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 or newer with glibc 2.8 or newer.

   New 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 an
   "eventfd()".

   Availability: See "eventfd()"

   New 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 an
   "eventfd()".

   Availability: See "eventfd()"

   New in version 3.10.

os.EFD_CLOEXEC

   Set close-on-exec flag for new "eventfd()" file descriptor.

   Availability: See "eventfd()"

   New in version 3.10.

os.EFD_NONBLOCK

   Set "O_NONBLOCK" status flag for new "eventfd()" file descriptor.

   Availability: See "eventfd()"

   New in version 3.10.

os.EFD_SEMAPHORE

   Provide semaphore-like semantics for reads from a "eventfd()" file
   descriptor. On read the internal counter is decremented by one.

   Availability: Linux 2.6.30 or newer with glibc 2.8 or newer.

   New in version 3.10.


Linux extended attributes
-------------------------

New 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 arguments "path",
   "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 argument "path".

   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 arguments "path",
   "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 be "XATTR_REPLACE" or "XATTR_CREATE". If
   "XATTR_REPLACE" is given and the attribute does not exist,
   "ENODATA" will be raised. If "XATTR_CREATE" is given and the
   attribute already exists, the attribute will not be created and
   "EEXISTS" 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 arguments "path",
   "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 of "3".  Be aware that calling
   this function will not call the Python signal handler registered
   for "SIGABRT" with "signal.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 by "ctypes".

   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 argument
   "path".

   Availability: Windows.

   New 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 as
   "AddDllDirectory" 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()"
   or "os.fsync()" before calling an "exec*" 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 the "execl*()" 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()", and "execvpe()") will use the "PATH"
   environment variable to locate the program *file*.  When the
   environment is being replaced (using one of the "exec*e" variants,
   discussed in the next paragraph), the new environment is used as
   the source of the "PATH" variable. The other variants, "execl()",
   "execle()", "execv()", and "execve()", will not use the "PATH"
   variable to locate the executable; *path* must contain an
   appropriate absolute or relative path.

   For "execle()", "execlpe()", "execve()", and "execvpe()" (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
   functions "execl()", "execlp()", "execv()", and "execvp()" 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
   using "os.supports_fd". If it is unavailable, using it will raise a
   "NotImplementedError".

   Raises an auditing event "os.exec" with arguments "path", "args",
   "env".

   Availability: Unix, Windows.

   New 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 a "fork()".

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.

   Availability: Unix.

os.EX_USAGE

   Exit code that means the command was used incorrectly, such as when
   the wrong number of arguments are given.

   Availability: Unix.

os.EX_DATAERR

   Exit code that means the input data was incorrect.

   Availability: Unix.

os.EX_NOINPUT

   Exit code that means an input file did not exist or was not
   readable.

   Availability: Unix.

os.EX_NOUSER

   Exit code that means a specified user did not exist.

   Availability: Unix.

os.EX_NOHOST

   Exit code that means a specified host did not exist.

   Availability: Unix.

os.EX_UNAVAILABLE

   Exit code that means that a required service is unavailable.

   Availability: Unix.

os.EX_SOFTWARE

   Exit code that means an internal software error was detected.

   Availability: Unix.

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.

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.

os.EX_CANTCREAT

   Exit code that means a user specified output file could not be
   created.

   Availability: Unix.

os.EX_IOERR

   Exit code that means that an error occurred while doing I/O on some
   file.

   Availability: Unix.

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.

os.EX_PROTOCOL

   Exit code that means that a protocol exchange was illegal, invalid,
   or not understood.

   Availability: Unix.

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.

os.EX_CONFIG

   Exit code that means that some kind of configuration error
   occurred.

   Availability: Unix.

os.EX_NOTFOUND

   Exit code that means something like "an entry was not found".

   Availability: Unix.

os.fork()

   Fork a child process.  Return "0" in the child and the child's
   process id in the parent.  If an error occurs "OSError" 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.

   Changed in version 3.8: Calling "fork()" in a subinterpreter is no
   longer supported ("RuntimeError" is raised).

   Warning:

     See "ssl" for applications that use the SSL module with fork().

   Availability: Unix.

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* is
   "0" 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 the "pty" module.  If
   an error occurs "OSError" is raised.

   Raises an auditing event "os.forkpty" with no arguments.

   Changed in version 3.8: Calling "forkpty()" in a subinterpreter is
   no longer supported ("RuntimeError" is raised).

   Availability: some flavors of Unix.

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" and "signal.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 of "kill()"
   additionally takes process handles to be killed.

   See also "signal.pthread_kill()".

   Raises an auditing event "os.kill" with arguments "pid", "sig".

   New in version 3.2: Windows support.

os.killpg(pgid, sig)

   Send the signal *sig* to the process group *pgid*.

   Raises an auditing event "os.killpg" with arguments "pgid", "sig".

   Availability: Unix.

os.nice(increment)

   Add *increment* to the process's "niceness".  Return the new
   niceness.

   Availability: Unix.

os.pidfd_open(pid, flags=0)

   Return a file descriptor referring to the process *pid*.  This
   descriptor can be used to perform process management without races
   and signals.  The *flags* argument is provided for future
   extensions; no flag values are currently defined.

   See the *pidfd_open(2)* man page for more details.

   Availability: Linux 5.3+

   New in version 3.9.

os.plock(op)

   Lock program segments into memory.  The value of *op* (defined in
   "<sys/lock.h>") determines which segments are locked.

   Availability: Unix.

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 has the same meaning as the corresponding
   argument to the built-in "open()" function. The returned file
   object reads or writes text strings rather than bytes.

   The "close" method returns "None" 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 the
   "close" method result (exit status) into an exit code if it is not
   "None". On Windows, the "close" method result is directly the exit
   code (or "None").

   This is implemented using "subprocess.Popen"; see that class's
   documentation for more powerful ways to manage and communicate with
   subprocesses.

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 of
   "posix_spawn()".

   The positional-only arguments *path*, *args*, and *env* are similar
   to "execve()".

   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()" and "exec()" 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)".

   These tuples correspond to the C library
   "posix_spawn_file_actions_addopen()",
   "posix_spawn_file_actions_addclose()", and
   "posix_spawn_file_actions_adddup2()" API calls used to prepare for
   the "posix_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 is "False", 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 library
   "POSIX_SPAWN_RESETIDS" flag.

   If the *setsid* argument is "True", it will create a new session ID
   for *posix_spawn*. *setsid* requires "POSIX_SPAWN_SETSID" or
   "POSIX_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 of "None" in the place of the
   scheduler policy indicates that is not being provided. This
   argument is a combination of the C library
   "POSIX_SPAWN_SETSCHEDPARAM" and "POSIX_SPAWN_SETSCHEDULER" flags.

   Raises an auditing event "os.posix_spawn" with arguments "path",
   "argv", "env".

   New in version 3.8.

   Availability: Unix.

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 the
   "PATH" environment variable (in the same way as for "execvp(3)").

   Raises an auditing event "os.posix_spawn" with arguments "path",
   "argv", "env".

   New in version 3.8.

   Availability: 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 calls "PyOS_BeforeFork()",
   "PyOS_AfterFork_Parent()" and "PyOS_AfterFork_Child()".

   There is no way to unregister a function.

   Availability: Unix.

   New 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* is "P_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 the "waitpid()"
   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 the "spawnl*()" 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()", and "spawnvpe()") will use the "PATH"
   environment variable to locate the program *file*.  When the
   environment is being replaced (using one of the "spawn*e" variants,
   discussed in the next paragraph), the new environment is used as
   the source of the "PATH" variable.  The other variants, "spawnl()",
   "spawnle()", "spawnv()", and "spawnve()", will not use the "PATH"
   variable to locate the executable; *path* must contain an
   appropriate absolute or relative path.

   For "spawnle()", "spawnlpe()", "spawnve()", and "spawnvpe()" (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 functions "spawnl()", "spawnlp()", "spawnv()",
   and "spawnvp()" 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 of "127".

   As an example, the following calls to "spawnlp()" and "spawnvpe()"
   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 arguments "mode", "path",
   "args", "env".

   Availability: Unix, Windows.  "spawnlp()", "spawnlpe()",
   "spawnvp()" and "spawnvpe()" are not available on Windows.
   "spawnle()" and "spawnve()" are not thread-safe on Windows; we
   advise you to use the "subprocess" module instead.

   Changed in version 3.6: Accepts a *path-like object*.

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, the "spawn*()"
   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*, the "spawn*()" 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 to "P_NOWAIT", but the new process is
   detached from the console of the calling process. If "P_OVERLAY" is
   used, the current process will be replaced; the "spawn*" 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 or "'open'", 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 "'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 ("'/'")  Use "pathlib" or the "os.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 arguments "path",
   "operation".

   Raises an auditing event "os.startfile/2" with arguments "path",
   "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 to "sys.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 preferable to using this function.  See the Replacing
   Older Functions with the subprocess Module section in the
   "subprocess" 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 argument "command".

   Availability: Unix, Windows.

os.times()

   Returns the current global process times. The return value is an
   object with five attributes:

   * "user" - user time

   * "system" - system time

   * "children_user" - user time of all child processes

   * "children_system" - system time of all child processes

   * "elapsed" - 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", and "elapsed" 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" and "system" 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.

   "waitstatus_to_exitcode()" can be used to convert the exit status
   into an exit code.

   Availability: Unix.

   See also:

     "waitpid()" can be used to wait for the completion of a specific
     child process and has more options.

os.waitid(idtype, id, options)

   Wait for the completion of one or more child processes. *idtype*
   can be "P_PID", "P_PGID", "P_ALL", or "P_PIDFD" on Linux. *id*
   specifies the pid to wait on. *options* is constructed from the
   ORing of one or more of "WEXITED", "WSTOPPED" or "WCONTINUED" and
   additionally may be ORed with "WNOHANG" or "WNOWAIT". The return
   value is an object representing the data contained in the
   "siginfo_t" structure, namely: "si_pid", "si_uid", "si_signo",
   "si_status", "si_code" or "None" if "WNOHANG" is specified and
   there are no children in a waitable state.

   Availability: Unix.

   New in version 3.3.

os.P_PID
os.P_PGID
os.P_ALL

   These are the possible values for *idtype* in "waitid()". They
   affect how *id* is interpreted.

   Availability: Unix.

   New in version 3.3.

os.P_PIDFD

   This is a Linux-specific *idtype* that indicates that *id* is a
   file descriptor that refers to a process.

   Availability: Linux 5.4+

   New in version 3.9.

os.WEXITED
os.WSTOPPED
os.WNOWAIT

   Flags that can be used in *options* in "waitid()" that specify what
   child signal to wait for.

   Availability: Unix.

   New in version 3.3.

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
   by "waitid()".

   Availability: Unix.

   New in version 3.3.

   Changed in version 3.9: Added "CLD_KILLED" and "CLD_STOPPED"
   values.

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 be
   "0" for normal operation.

   If *pid* is greater than "0", "waitpid()" requests status
   information for that specific process.  If *pid* is "0", 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*).

   An "OSError" is raised with the value of errno when the syscall
   returns -1.

   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. The "spawn*"
   functions called with "P_NOWAIT" return suitable process handles.

   "waitstatus_to_exitcode()" can be used to convert the exit status
   into an exit code.

   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 to
   "resource"."getrusage()" for details on resource usage information.
   The option argument is the same as that provided to "waitpid()" and
   "wait4()".

   "waitstatus_to_exitcode()" can be used to convert the exit status
   into an exitcode.

   Availability: Unix.

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 to "resource"."getrusage()" for
   details on resource usage information.  The arguments to "wait4()"
   are the same as those provided to "waitpid()".

   "waitstatus_to_exitcode()" can be used to convert the exit status
   into an exitcode.

   Availability: Unix.

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 (return "WEXITSTATUS(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 with "WUNTRACED" option, the caller must first check if
   "WIFSTOPPED(status)" is true. This function must not be called if
   "WIFSTOPPED(status)" is true.

   See also:

     "WIFEXITED()", "WEXITSTATUS()", "WIFSIGNALED()", "WTERMSIG()",
     "WIFSTOPPED()", "WSTOPSIG()" functions.

   New in version 3.9.

os.WNOHANG

   The option for "waitpid()" to return immediately if no child
   process status is available immediately. The function returns "(0,
   0)" in this case.

   Availability: Unix.

os.WCONTINUED

   This option causes child processes to be reported if they have been
   continued from a job control stop since their status was last
   reported.

   Availability: some Unix systems.

os.WUNTRACED

   This option causes child processes to be reported if they have been
   stopped but their current state has not been reported since they
   were stopped.

   Availability: Unix.

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 return "False".

   This function should be employed only if "WIFSIGNALED()" is true.

   Availability: Unix.

os.WIFCONTINUED(status)

   Return "True" if a stopped child has been resumed by delivery of
   "SIGCONT" (if the process has been continued from a job control
   stop), otherwise return "False".

   See "WCONTINUED" option.

   Availability: Unix.

os.WIFSTOPPED(status)

   Return "True" if the process was stopped by delivery of a signal,
   otherwise return "False".

   "WIFSTOPPED()" only returns "True" if the "waitpid()" call was done
   using "WUNTRACED" option or when the process is being traced (see
   *ptrace(2)*).

   Availability: Unix.

os.WIFSIGNALED(status)

   Return "True" if the process was terminated by a signal, otherwise
   return "False".

   Availability: Unix.

os.WIFEXITED(status)

   Return "True" if the process exited terminated normally, that is,
   by calling "exit()" or "_exit()", or by returning from "main()";
   otherwise return "False".

   Availability: Unix.

os.WEXITSTATUS(status)

   Return the process exit status.

   This function should be employed only if "WIFEXITED()" is true.

   Availability: Unix.

os.WSTOPSIG(status)

   Return the signal which caused the process to stop.

   This function should be employed only if "WIFSTOPPED()" is true.

   Availability: Unix.

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.


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.

New 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()", and "sched_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* (or the current
   process if zero) is restricted to.


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 in "confstr_names", an "OSError" is raised
   with "errno.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 CPUs in the system. Returns "None" if
   undetermined.

   This number is not equivalent to the number of CPUs the current
   process can use.  The number of usable CPUs can be obtained with
   "len(os.sched_getaffinity(0))"

   New in version 3.4.

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.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 for
   "confstr()" apply here as well; the dictionary that provides
   information on the known names is given by "sysconf_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.

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 via "os.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 via "os.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 --- use "os.path.split()" and
   "os.path.join()" --- but it is occasionally useful. Also available
   via "os.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 where "sep" is a
   backslash. Also available via "os.path".

os.extsep

   The character which separates the base filename from the extension;
   for example, the "'.'" in "os.py". Also available via "os.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 via "os.path".

os.defpath

   The default search path used by "exec*p*" and "spawn*p*" if the
   environment doesn't have a "'PATH'" key. Also available via
   "os.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 via "os.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()" and "getdlopenflags()"
   functions.  See the Unix manual page *dlopen(3)* for what the
   different flags mean.

   New 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" and
   "GRND_NONBLOCK".

   See also the Linux getrandom() manual page.

   Availability: Linux 3.17 and newer.

   New in version 3.6.

os.urandom(size)

   Return a string 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, the "getrandom()"
   function can be used to get random bytes in non-blocking mode
   (using the "GRND_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, the "NotImplementedError" exception is
   raised.

   On Windows, it will use "CryptGenRandom()".

   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 see "random.SystemRandom".

   Changed in version 3.6.0: On Linux, "getrandom()" is now used in
   blocking mode to increase the security.

   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 3.5: On Linux 3.17 and newer, the "getrandom()"
   syscall is now used when available.  On OpenBSD 5.6 and newer, the
   C "getentropy()" function is now used. These functions avoid the
   usage of an internal file descriptor.

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, then "getrandom()" does not
   block in these cases, but instead immediately raises
   "BlockingIOError".

   New 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.

   New in version 3.6.
