"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.

* 在 VxWorks 系统上，os.fork, os.execv 和 os.spawn*p* 都未支持。

備註: 如果使用无效或无法访问的文件名与路径，或者其他类型正确但操作系
  统不接 受的参数，此模块的所有函数都抛出 "OSError" （或者它的子类）。

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'".

   也參考: "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 file system encoding to
perform this conversion (see "sys.getfilesystemencoding()").

3.1 版更變: 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 may raise UnicodeErrors.


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.

   可用性: 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.

   If the platform supports the "putenv()" function, 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.

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

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

   If "putenv()" is not provided, a modified copy of this mapping  may
   be passed to the appropriate process-creation functions to cause
   child processes to use a modified environment.

   If the platform supports the "unsetenv()" function, 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.

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.

   3.2 版新加入.

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 with
   "'surrogateescape'" error handler, or "'strict'" on Windows; return
   "bytes" unchanged.

   "fsdecode()" is the reverse function.

   3.2 版新加入.

   3.6 版更變: Support added to accept objects implementing the
   "os.PathLike" interface.

os.fsdecode(filename)

   Decode the *path-like* *filename* from the filesystem encoding with
   "'surrogateescape'" error handler, or "'strict'" on Windows; return
   "str" unchanged.

   "fsencode()" is the reverse function.

   3.2 版新加入.

   3.6 版更變: 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.

   3.6 版新加入.

class os.PathLike

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

   3.6 版新加入.

   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.

   可用性: 大部分的Unix系统，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.

   可用性: 大部分的Unix系统。

   3.2 版新加入.

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.

   3.2 版新加入.

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.

   可用性: Unix。

os.geteuid()

   Return the current process's effective user id.

   可用性: Unix。

os.getgid()

   Return the real group id of the current process.

   可用性: 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*.

   可用性: Unix。

   3.3 版新加入.

os.getgroups()

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

   可用性: Unix。

   備註: 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.

   可用性: 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.

   可用性: Unix。

os.getpgrp()

   Return the id of the current process group.

   可用性: 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.

   可用性: Unix, Windows。

   3.2 版更變: 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.

   可用性: Unix。

   3.3 版新加入.

os.PRIO_PROCESS
os.PRIO_PGRP
os.PRIO_USER

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

   可用性: Unix。

   3.3 版新加入.

os.getresuid()

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

   可用性: Unix。

   3.2 版新加入.

os.getresgid()

   Return a tuple (rgid, egid, sgid) denoting the current process's
   real, effective, and saved group ids.

   可用性: Unix。

   3.2 版新加入.

os.getuid()

   Return the current process's real user id.

   可用性: 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.

   可用性: Unix。

   3.2 版新加入.

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()".

   可用性: 大部分的Unix系统，Windows。

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

   When "putenv()" is supported, 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".

os.setegid(egid)

   Set the current process's effective group id.

   可用性: Unix。

os.seteuid(euid)

   Set the current process's effective user id.

   可用性: Unix。

os.setgid(gid)

   Set the current process' group id.

   可用性: 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.

   可用性: Unix。

   備註: 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.

   可用性: 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.

   可用性: 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.

   可用性: Unix。

   3.3 版新加入.

os.setregid(rgid, egid)

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

   可用性: Unix。

os.setresgid(rgid, egid, sgid)

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

   可用性: Unix。

   3.2 版新加入.

os.setresuid(ruid, euid, suid)

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

   可用性: Unix。

   3.2 版新加入.

os.setreuid(ruid, euid)

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

   可用性: Unix。

os.getsid(pid)

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

   可用性: Unix。

os.setsid()

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

   可用性: Unix。

os.setuid(uid)

   Set the current process's user id.

   可用性: 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).

   3.2 版新加入.

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())".

   可用性: 较新的 Unix 版本。

   3.3 版更變: 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()".

   When "unsetenv()" is supported, 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".

   可用性: 大部分的Unix系统，Windows。


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

这些函数创建新的 *file objects* 。（参见 "open()" 以获取打开文件描述符
的相关信息。）

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*.

   備註: 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)

   从文件描述符 *src* 复制 *count* 字节，从偏移量 *offset_src* 开始读
   取，到文件描述符 *dst*，从偏移量 *offset_dst* 开始写入。如果
   *offset_src* 为 None，则 *src* 将从当前位置开始读取；*offset_dst*
   同理。*src* 和 *dst* 指向的文件必须处于相同的文件系统，否则将会抛出
   一个 "errno" 被设为 "errno.EXDEV" 的 "OSError" 。

   此复制的完成没有额外的从内核到用户空间再回到内核的数据转移花费。另
   外，一些文件系统可能实现额外的优化。完成复制就如同打开两个二进制文
   件一样。

   返回值是复制的字节的数目。这可能低于需求的数目。

   Availability: Linux kernel >= 4.5 或 glibc >= 2.27。

   3.8 版新加入.

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".

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.

   3.4 版更變: 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".

   3.4 版更變: Add the optional *inheritable* parameter.

   3.7 版更變: 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)".

   可用性: 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)".

   可用性: Unix。

os.fdatasync(fd)

   Force write of file with filedescriptor *fd* to disk. Does not
   force update of metadata.

   可用性: Unix。

   備註: 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)".

   可用性: 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)".

   也參考: 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)".

   可用性: 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.

   可用性: 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".

   可用性: Unix, Windows。

   3.5 版更變: 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()".

   可用性: Unix。

   3.5 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

os.F_LOCK
os.F_TLOCK
os.F_ULOCK
os.F_TEST

   Flags that specify what action "lockf()" will take.

   可用性: Unix。

   3.3 版新加入.

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.

   3.3 版新加入: Some operating systems could support additional
   values, like "os.SEEK_HOLE" or "os.SEEK_DATA".

os.open(path, flags, mode=0o777, *, dir_fd=None)

   Open the file *path* and set various flags according to *flags* and
   possibly its mode according to *mode*.  When computing *mode*, the
   current umask value is first masked out.  Return the file
   descriptor for the newly opened file. The new file descriptor is
   non-inheritable.

   For a description of the flag and mode values, see the C run-time
   documentation; flag constants (like "O_RDONLY" 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".

   3.4 版更變: The new file descriptor is now non-inheritable.

   備註: 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()".

   3.3 版新加入: The *dir_fd* argument.

   3.5 版更變: 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).

   3.6 版更變: 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.

   3.3 版更變: 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_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.

   3.4 版更變: 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.

   可用性: 某些 Unix。

   3.4 版更變: 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.

   可用性: Unix, Windows。

   3.4 版更變: 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.

   可用性: 某些 Unix。

   3.3 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

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".

   可用性: Unix。

   3.3 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

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. Using flags requires Linux 4.6 or newer.

   3.7 版新加入.

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.

   3.7 版新加入.

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.

   3.7 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

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"

   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. Using flags requires Linux 4.7 or newer.

   3.7 版新加入.

os.RWF_DSYNC

   Provide a per-write equivalent of the "O_DSYNC" "open(2)" flag.
   This flag effect applies only to the data range written by the
   system call.

   Availability: Linux 4.7 and newer.

   3.7 版新加入.

os.RWF_SYNC

   Provide a per-write equivalent of the "O_SYNC" "open(2)" flag. This
   flag effect applies only to the data range written by the system
   call.

   Availability: Linux 4.7 and newer.

   3.7 版新加入.

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.

   備註: 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.

   3.5 版更變: 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, in, offset, count)
os.sendfile(out, in, offset, count[, headers][, trailers], flags=0)

   Copy *count* bytes from file descriptor *in* to file descriptor
   *out* 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* and the position of *in* 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* 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* is reached.

   All platforms support sockets as *out* 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.

   可用性: Unix。

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

   3.3 版新加入.

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()".

   可用性: Unix。

   3.5 版新加入.

os.SF_NODISKIO
os.SF_MNOWAIT
os.SF_SYNC

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

   可用性: Unix。

   3.3 版新加入.

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.

   可用性: Unix。

   3.3 版新加入.

os.tcgetpgrp(fd)

   Return the process group associated with the terminal given by *fd*
   (an open file descriptor as returned by "os.open()").

   可用性: 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*.

   可用性: 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.

   可用性: Unix。

os.write(fd, str)

   Write the bytestring in *str* to file descriptor *fd*.

   Return the number of bytes actually written.

   備註: 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.

   3.5 版更變: 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.

   可用性: Unix。

   3.3 版新加入.


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

3.3 版新加入.

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.

   可用性: 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
-------------------------------

3.4 版新加入.

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).

   可用性: Windows。

os.set_handle_inheritable(handle, inheritable)

   Set the "inheritable" flag of the specified handle.

   可用性: 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".

   備註: 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()

   備註: 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.

   3.3 版更變: Added the *dir_fd*, *effective_ids*, and
   *follow_symlinks* parameters.

   3.6 版更變: 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".

   3.3 版新加入: Added support for specifying *path* as a file
   descriptor on some platforms.

   3.6 版更變: 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.

   可用性: Unix。

   3.3 版新加入: The *follow_symlinks* argument.

   3.6 版更變: 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.

   備註: 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.

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor, and the *dir_fd* and *follow_symlinks* arguments.

   3.6 版更變: 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.

   可用性: Unix。

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor, and the *dir_fd* and *follow_symlinks* arguments.

   3.6 版更變: Supports a *path-like object*.

os.chroot(path)

   Change the root directory of the current process to *path*.

   可用性: Unix。

   3.6 版更變: 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)".

   可用性: Unix。

os.getcwd()

   Return a string representing the current working directory.

os.getcwdb()

   Return a bytestring representing the current working directory.

   3.8 版更變: 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)".

   可用性: Unix。

   3.6 版更變: 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)".

   可用性: Unix。

   3.6 版更變: 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)".

   可用性: Unix。

   3.6 版更變: 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.

   可用性: Unix, Windows。

   3.2 版更變: Added Windows support.

   3.3 版新加入: Added the *src_dir_fd*, *dst_dir_fd*, and
   *follow_symlinks* arguments.

   3.6 版更變: 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.

   *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".

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

   也參考: The "scandir()" function returns directory entries along
     with file attribute information, giving better performance for
     many common use cases.

   3.2 版更變: The *path* parameter became optional.

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor.

   3.6 版更變: 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.

   也參考: The "stat()" function.

   3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

   3.3 版更變: Added the *dir_fd* parameter.

   3.6 版更變: Accepts a *path-like object* for *src* and *dst*.

   3.8 版更變: On Windows, now opens reparse points that represent
   another path (name surrogates), including symbolic links and
   directory junctions. Other kinds of reparse points are resolved by
   the operating system as for "stat()".

os.mkdir(path, mode=0o777, *, dir_fd=None)

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

   If the directory already exists, "FileExistsError" is raised.

   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.

   3.3 版新加入: The *dir_fd* argument.

   3.6 版更變: Accepts a *path-like object*.

os.makedirs(name, mode=0o777, exist_ok=False)

   Recursive directory creation function.  Like "mkdir()", but makes
   all intermediate-level directories needed to contain the leaf
   directory.

   The *mode* parameter is passed to "mkdir()" for creating the leaf
   directory; see the mkdir() description for how it is interpreted.
   To set the file permission bits of any newly-created parent
   directories you can set the umask before 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.

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

   This function handles UNC paths correctly.

   3.2 版新加入: The *exist_ok* parameter.

   3.4.1 版更變: 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.

   3.6 版更變: Accepts a *path-like object*.

   3.7 版更變: The *mode* argument no longer affects the file
   permission bits of newly-created intermediate-level directories.

os.mkfifo(path, mode=0o666, *, dir_fd=None)

   Create a FIFO (a named pipe) named *path* with numeric mode *mode*.
   The current umask value is first masked out from the mode.

   This function can also support paths relative to directory
   descriptors.

   FIFOs are pipes that can be accessed like regular files.  FIFOs
   exist until they are deleted (for example with "os.unlink()").
   Generally, FIFOs are used as rendezvous between "client" and
   "server" type processes: the server opens the FIFO for reading, and
   the client opens it for writing.  Note that "mkfifo()" doesn't open
   the FIFO --- it just creates the rendezvous point.

   可用性: Unix。

   3.3 版新加入: The *dir_fd* argument.

   3.6 版更變: Accepts a *path-like object*.

os.mknod(path, mode=0o600, device=0, *, dir_fd=None)

   Create a filesystem node (file, device special file or named pipe)
   named *path*. *mode* specifies both the permissions to use and the
   type of node to be created, being combined (bitwise OR) with one of
   "stat.S_IFREG", "stat.S_IFCHR", "stat.S_IFBLK", 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.

   可用性: Unix。

   3.3 版新加入: The *dir_fd* argument.

   3.6 版更變: 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.

   可用性: Unix。

   3.6 版更變: 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.

   可用性: 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.

   可用性: Unix, Windows。

   3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

   3.3 版新加入: The *dir_fd* argument.

   3.6 版更變: Accepts a *path-like object* on Unix.

   3.8 版更變: Accepts a *path-like object* and a bytes object on
   Windows.

   3.8 版更變: 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.

   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()".

   3.3 版新加入: The *dir_fd* argument.

   3.6 版更變: 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.

   3.6 版更變: 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()".

   3.3 版新加入: The *src_dir_fd* and *dst_dir_fd* arguments.

   3.6 版更變: 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()".

   備註: This function can fail with the new directory structure
     made if you lack permissions needed to remove the leaf directory
     or file.

   3.6 版更變: 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.

   3.3 版新加入.

   3.6 版更變: 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.

   3.3 版新加入: The *dir_fd* parameter.

   3.6 版更變: 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.

   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.

      3.6 版新加入.

   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)

   備註: On Unix-based systems, "scandir()" uses the system's
     opendir() and readdir() functions. On Windows, it uses the Win32
     FindFirstFileW and FindNextFileW functions.

   3.5 版新加入.

   3.6 版新加入: 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*.

   3.7 版更變: 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.

   3.5 版新加入.

   3.6 版更變: 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

   也參考: "fstat()" and "lstat()" functions.

   3.3 版新加入: Added the *dir_fd* and *follow_symlinks* arguments,
   specifying a file descriptor instead of a path.

   3.6 版更變: Accepts a *path-like object*.

   3.8 版更變: 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.

   備註: 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.

   3.3 版新加入: Added the "st_atime_ns", "st_mtime_ns", and
   "st_ctime_ns" members.

   3.5 版新加入: Added the "st_file_attributes" member on Windows.

   3.5 版更變: Windows now returns the file index as "st_ino" when
   available.

   3.7 版新加入: Added the "st_fstype" member to Solaris/derivatives.

   3.8 版新加入: Added the "st_reparse_tag" member on Windows.

   3.8 版更變: 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.

   可用性: Unix。

   3.2 版更變: The "ST_RDONLY" and "ST_NOSUID" constants were added.

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor.

   3.4 版更變: 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.

   3.6 版更變: Accepts a *path-like object*.

   3.7 版新加入: 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.

   3.3 版新加入.

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.

   3.3 版新加入.

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

   3.3 版新加入.

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

   3.3 版新加入.

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.

   備註: 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.

   可用性: Unix, Windows。

   3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

   3.3 版新加入: Added the *dir_fd* argument, and now allow
   *target_is_directory* on non-Windows platforms.

   3.6 版更變: Accepts a *path-like object* for *src* and *dst*.

   3.8 版更變: Added support for unelevated symlinks on Windows with
   Developer Mode.

os.sync()

   Force write of everything to disk.

   可用性: Unix。

   3.3 版新加入.

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".

   可用性: Unix, Windows。

   3.3 版新加入.

   3.5 版更變: Added support for Windows

   3.6 版更變: 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.

   3.3 版新加入: The *dir_fd* parameter.

   3.6 版更變: 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.

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor, and the *dir_fd*, *follow_symlinks*, and *ns*
   parameters.

   3.6 版更變: 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)".

   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.

   備註: 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.

   備註: 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))

   3.5 版更變: This function now calls "os.scandir()" instead of
   "os.listdir()", making it faster by reducing the number of calls to
   "os.stat()".

   3.6 版更變: 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".

   備註: 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)

   可用性: Unix。

   3.3 版新加入.

   3.6 版更變: Accepts a *path-like object*.

   3.7 版更變: 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.

   3.8 版新加入.

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.

   3.8 版新加入.


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

3.3 版新加入.

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.

   3.6 版更變: 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.

   3.6 版更變: 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.

   This function can support specifying a file descriptor and not
   following symlinks.

   3.6 版更變: 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.  *flags* may be
   "XATTR_REPLACE" or "XATTR_CREATE". If "XATTR_REPLACE" is given and
   the attribute does not exist, "EEXISTS" will be raised. If
   "XATTR_CREATE" is given and the attribute already exists, the
   attribute will not be created and "ENODATA" will be raised.

   This function can support specifying a file descriptor and not
   following symlinks.

   備註: A bug in Linux kernel versions less than 2.6.39 caused the
     flags argument to be ignored on some filesystems.

   3.6 版更變: 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.

   可用性: Windows。

   3.8 版新加入: 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".

   可用性: Unix, Windows。

   3.3 版新加入: Added support for specifying *path* as an open file
   descriptor for "execve()".

   3.6 版更變: Accepts a *path-like object*.

os._exit(n)

   Exit the process with status *n*, without calling cleanup handlers,
   flushing stdio buffers, etc.

   備註: 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.

備註: 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.

   可用性: Unix。

os.EX_USAGE

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

   可用性: Unix。

os.EX_DATAERR

   Exit code that means the input data was incorrect.

   可用性: Unix。

os.EX_NOINPUT

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

   可用性: Unix。

os.EX_NOUSER

   Exit code that means a specified user did not exist.

   可用性: Unix。

os.EX_NOHOST

   Exit code that means a specified host did not exist.

   可用性: Unix。

os.EX_UNAVAILABLE

   Exit code that means that a required service is unavailable.

   可用性: Unix。

os.EX_SOFTWARE

   Exit code that means an internal software error was detected.

   可用性: Unix。

os.EX_OSERR

   Exit code that means an operating system error was detected, such
   as the inability to fork or create a pipe.

   可用性: 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.

   可用性: Unix。

os.EX_CANTCREAT

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

   可用性: Unix。

os.EX_IOERR

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

   可用性: 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.

   可用性: Unix。

os.EX_PROTOCOL

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

   可用性: Unix。

os.EX_NOPERM

   Exit code that means that there were insufficient permissions to
   perform the operation (but not intended for file system problems).

   可用性: Unix。

os.EX_CONFIG

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

   可用性: Unix。

os.EX_NOTFOUND

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

   可用性: 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.

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

   可用性: 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.

   可用性: 某些 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()".

   3.2 版新加入: Windows support.

os.killpg(pgid, sig)

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

   可用性: Unix。

os.nice(increment)

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

   可用性: Unix。

os.plock(op)

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

   可用性: 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.

   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.

   3.8 版新加入.

   可用性: 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)").

   3.8 版新加入.

   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.

   可用性: Unix。

   3.7 版新加入.

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)

   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.

   3.6 版更變: 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.

   可用性: 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.

   可用性: 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.

   可用性: Windows。

os.startfile(path[, operation])

   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).

   "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.  If you want to use
   an absolute path, make sure the first character is not a slash
   ("'/'"); the underlying Win32 "ShellExecute()" function doesn't
   work if it is.  Use the "os.path.normpath()" function to ensure
   that the path is 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.

   可用性: Windows。

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.

   On Unix, the return value is the exit status of the process encoded
   in the format specified for "wait()".  Note that POSIX does not
   specify the meaning of the return value of the C "system()"
   function, so the return value of the Python function is system-
   dependent.

   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.

   Raises an auditing event "os.system" with argument "command".

   可用性: 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
   <https://docs.microsoft.com/windows/win32/api/processthreadsapi/nf-
   processthreadsapi-getprocesstimes>* _ on Windows. On Windows, only
   "user" and "system" are known; the other attributes are zero.

   可用性: Unix, Windows。

   3.3 版更變: 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.

   可用性: Unix。

os.waitid(idtype, id, options)

   Wait for the completion of one or more child processes. *idtype*
   can be "P_PID", "P_PGID" or "P_ALL". *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.

   可用性: Unix。

   3.3 版新加入.

os.P_PID
os.P_PGID
os.P_ALL

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

   可用性: Unix。

   3.3 版新加入.

os.WEXITED
os.WSTOPPED
os.WNOWAIT

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

   可用性: Unix。

   3.3 版新加入.

os.CLD_EXITED
os.CLD_DUMPED
os.CLD_TRAPPED
os.CLD_CONTINUED

   These are the possible values for "si_code" in the result returned
   by "waitid()".

   可用性: Unix。

   3.3 版新加入.

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.

   3.5 版更變: 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()".

   可用性: 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()".

   可用性: Unix。

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.

   可用性: 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.

   可用性: 部分 Unix 系统。

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.

   可用性: 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".

   可用性: Unix。

os.WIFCONTINUED(status)

   Return "True" if the process has been continued from a job control
   stop, otherwise return "False".

   可用性: Unix。

os.WIFSTOPPED(status)

   Return "True" if the process has been stopped, otherwise return
   "False".

   可用性: Unix。

os.WIFSIGNALED(status)

   Return "True" if the process exited due to a signal, otherwise
   return "False".

   可用性: Unix。

os.WIFEXITED(status)

   Return "True" if the process exited using the *exit(2)* system
   call, otherwise return "False".

   可用性: Unix。

os.WEXITSTATUS(status)

   If "WIFEXITED(status)" is true, return the integer parameter to the
   *exit(2)* system call.  Otherwise, the return value is meaningless.

   可用性: Unix。

os.WSTOPSIG(status)

   Return the signal which caused the process to stop.

   可用性: Unix。

os.WTERMSIG(status)

   Return the signal which caused the process to exit.

   可用性: 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.

3.3 版新加入.

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 a 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.

   可用性: 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.

   可用性: 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))"

   3.4 版新加入.

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.

   可用性: 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".

   可用性: 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.

   可用性: 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.

   3.3 版新加入.


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.

   3.6 版新加入.

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()".

   也參考: 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".

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

   3.5.2 版更變: On Linux, if the "getrandom()" syscall blocks (the
   urandom entropy pool is not initialized yet), fall back on reading
   "/dev/urandom".

   3.5 版更變: 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".

   3.6 版新加入.

os.GRND_RANDOM

   If  this  bit  is  set,  then  random bytes are drawn from the
   "/dev/random" pool instead of the "/dev/urandom" pool.

   3.6 版新加入.
