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+
+:mod:`os` --- Miscellaneous operating system interfaces
+=======================================================
+
+.. module:: os
+ :synopsis: Miscellaneous operating system interfaces.
+
+
+This module provides a more portable way of using operating system dependent
+functionality than importing a operating system dependent built-in module like
+:mod:`posix` or :mod:`nt`. (If you just want to read or write a file see
+:func:`open`, and if you want to manipulate paths, see the :mod:`os.path`
+module.)
+
+This module searches for an operating system dependent built-in module like
+:mod:`mac` or :mod:`posix` and exports the same functions and data as found
+there. The design of all Python's built-in operating system dependent modules
+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 :mod:`os` module, but using them is of course a threat to portability!
+
+Note that after the first time :mod:`os` is imported, there is *no* performance
+penalty in using functions from :mod:`os` instead of directly from the operating
+system dependent built-in module, so there should be *no* reason not to use
+:mod:`os`!
+
+The :mod:`os` module contains many functions and data values. The items below
+and in the following sub-sections are all available directly from the :mod:`os`
+module.
+
+.. % Frank Stajano <fstajano@uk.research.att.com> complained that it
+.. % wasn't clear that the entries described in the subsections were all
+.. % available at the module level (most uses of subsections are
+.. % different); I think this is only a problem for the HTML version,
+.. % where the relationship may not be as clear.
+.. %
+
+
+.. exception:: error
+
+ .. index:: module: errno
+
+ This exception is raised when a function returns a system-related error (not for
+ illegal argument types or other incidental errors). This is also known as the
+ built-in exception :exc:`OSError`. The accompanying value is a pair containing
+ the numeric error code from :cdata:`errno` and the corresponding string, as
+ would be printed by the C function :cfunc:`perror`. See the module
+ :mod:`errno`, which contains names for the error codes defined by the underlying
+ operating system.
+
+ When exceptions are classes, this exception carries two attributes,
+ :attr:`errno` and :attr:`strerror`. The first holds the value of the C
+ :cdata:`errno` variable, and the latter holds the corresponding error message
+ from :cfunc:`strerror`. For exceptions that involve a file system path (such as
+ :func:`chdir` or :func:`unlink`), the exception instance will contain a third
+ attribute, :attr:`filename`, which is the file name passed to the function.
+
+
+.. data:: name
+
+ The name of the operating system dependent module imported. The following names
+ have currently been registered: ``'posix'``, ``'nt'``, ``'mac'``, ``'os2'``,
+ ``'ce'``, ``'java'``, ``'riscos'``.
+
+
+.. data:: path
+
+ The corresponding operating system dependent standard module for pathname
+ operations, such as :mod:`posixpath` or :mod:`macpath`. Thus, given the proper
+ imports, ``os.path.split(file)`` is equivalent to but more portable than
+ ``posixpath.split(file)``. Note that this is also an importable module: it may
+ be imported directly as :mod:`os.path`.
+
+
+.. _os-procinfo:
+
+Process Parameters
+------------------
+
+These functions and data items provide information and operate on the current
+process and user.
+
+
+.. data:: 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 :mod:`os` module is imported,
+ typically during Python startup as part of processing :file:`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 :func:`putenv` function, this mapping may be used
+ to modify the environment as well as query the environment. :func:`putenv` will
+ be called automatically when the mapping is modified.
+
+ .. note::
+
+ Calling :func:`putenv` directly does not change ``os.environ``, so it's better
+ to modify ``os.environ``.
+
+ .. note::
+
+ On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may cause
+ memory leaks. Refer to the system documentation for :cfunc:`putenv`.
+
+ If :func:`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 :func:`unsetenv` function, you can delete items in
+ this mapping to unset environment variables. :func:`unsetenv` will be called
+ automatically when an item is deleted from ``os.environ``.
+
+
+.. function:: chdir(path)
+ fchdir(fd)
+ getcwd()
+ :noindex:
+
+ These functions are described in :ref:`os-file-dir`.
+
+
+.. function:: ctermid()
+
+ Return the filename corresponding to the controlling terminal of the process.
+ Availability: Unix.
+
+
+.. function:: getegid()
+
+ Return the effective group id of the current process. This corresponds to the
+ 'set id' bit on the file being executed in the current process. Availability:
+ Unix.
+
+
+.. function:: geteuid()
+
+ .. index:: single: user; effective id
+
+ Return the current process' effective user id. Availability: Unix.
+
+
+.. function:: getgid()
+
+ .. index:: single: process; group
+
+ Return the real group id of the current process. Availability: Unix.
+
+
+.. function:: getgroups()
+
+ Return list of supplemental group ids associated with the current process.
+ Availability: Unix.
+
+
+.. function:: 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 the environment variable
+ :envvar:`LOGNAME` to find out who the user is, or
+ ``pwd.getpwuid(os.getuid())[0]`` to get the login name of the currently
+ effective user ID. Availability: Unix.
+
+
+.. function:: getpgid(pid)
+
+ Return the process group id of the process with process id *pid*. If *pid* is 0,
+ the process group id of the current process is returned. Availability: Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: getpgrp()
+
+ .. index:: single: process; group
+
+ Return the id of the current process group. Availability: Unix.
+
+
+.. function:: getpid()
+
+ .. index:: single: process; id
+
+ Return the current process id. Availability: Unix, Windows.
+
+
+.. function:: getppid()
+
+ .. index:: single: process; id of parent
+
+ Return the parent's process id. Availability: Unix.
+
+
+.. function:: getuid()
+
+ .. index:: single: user; id
+
+ Return the current process' user id. Availability: Unix.
+
+
+.. function:: getenv(varname[, value])
+
+ Return the value of the environment variable *varname* if it exists, or *value*
+ if it doesn't. *value* defaults to ``None``. Availability: most flavors of
+ Unix, Windows.
+
+
+.. function:: putenv(varname, value)
+
+ .. index:: single: environment variables; setting
+
+ Set the environment variable named *varname* to the string *value*. Such
+ changes to the environment affect subprocesses started with :func:`os.system`,
+ :func:`popen` or :func:`fork` and :func:`execv`. Availability: most flavors of
+ Unix, Windows.
+
+ .. note::
+
+ On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may cause
+ memory leaks. Refer to the system documentation for putenv.
+
+ When :func:`putenv` is supported, assignments to items in ``os.environ`` are
+ automatically translated into corresponding calls to :func:`putenv`; however,
+ calls to :func:`putenv` don't update ``os.environ``, so it is actually
+ preferable to assign to items of ``os.environ``.
+
+
+.. function:: setegid(egid)
+
+ Set the current process's effective group id. Availability: Unix.
+
+
+.. function:: seteuid(euid)
+
+ Set the current process's effective user id. Availability: Unix.
+
+
+.. function:: setgid(gid)
+
+ Set the current process' group id. Availability: Unix.
+
+
+.. function:: 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 typical available only to the superuser.
+ Availability: Unix.
+
+ .. versionadded:: 2.2
+
+
+.. function:: setpgrp()
+
+ Calls the system call :cfunc:`setpgrp` or :cfunc:`setpgrp(0, 0)` depending on
+ which version is implemented (if any). See the Unix manual for the semantics.
+ Availability: Unix.
+
+
+.. function:: setpgid(pid, pgrp)
+
+ Calls the system call :cfunc:`setpgid` to set the process group id of the
+ process with id *pid* to the process group with id *pgrp*. See the Unix manual
+ for the semantics. Availability: Unix.
+
+
+.. function:: setreuid(ruid, euid)
+
+ Set the current process's real and effective user ids. Availability: Unix.
+
+
+.. function:: setregid(rgid, egid)
+
+ Set the current process's real and effective group ids. Availability: Unix.
+
+
+.. function:: getsid(pid)
+
+ Calls the system call :cfunc:`getsid`. See the Unix manual for the semantics.
+ Availability: Unix.
+
+ .. versionadded:: 2.4
+
+
+.. function:: setsid()
+
+ Calls the system call :cfunc:`setsid`. See the Unix manual for the semantics.
+ Availability: Unix.
+
+
+.. function:: setuid(uid)
+
+ .. index:: single: user; id, setting
+
+ Set the current process' user id. Availability: Unix.
+
+.. % placed in this section since it relates to errno.... a little weak
+
+
+.. function:: strerror(code)
+
+ Return the error message corresponding to the error code in *code*.
+ Availability: Unix, Windows.
+
+
+.. function:: umask(mask)
+
+ Set the current numeric umask and returns the previous umask. Availability:
+ Unix, Windows.
+
+
+.. function:: uname()
+
+ .. index::
+ single: gethostname() (in module socket)
+ single: gethostbyaddr() (in module socket)
+
+ Return a 5-tuple containing information identifying the current operating
+ system. The tuple contains 5 strings: ``(sysname, nodename, release, version,
+ machine)``. Some systems truncate the nodename to 8 characters or to the
+ leading component; a better way to get the hostname is
+ :func:`socket.gethostname` or even
+ ``socket.gethostbyaddr(socket.gethostname())``. Availability: recent flavors of
+ Unix.
+
+
+.. function:: unsetenv(varname)
+
+ .. index:: single: environment variables; deleting
+
+ Unset (delete) the environment variable named *varname*. Such changes to the
+ environment affect subprocesses started with :func:`os.system`, :func:`popen` or
+ :func:`fork` and :func:`execv`. Availability: most flavors of Unix, Windows.
+
+ When :func:`unsetenv` is supported, deletion of items in ``os.environ`` is
+ automatically translated into a corresponding call to :func:`unsetenv`; however,
+ calls to :func:`unsetenv` don't update ``os.environ``, so it is actually
+ preferable to delete items of ``os.environ``.
+
+
+.. _os-newstreams:
+
+File Object Creation
+--------------------
+
+These functions create new file objects. (See also :func:`open`.)
+
+
+.. function:: fdopen(fd[, mode[, bufsize]])
+
+ .. index:: single: I/O control; buffering
+
+ Return an open file object connected to the file descriptor *fd*. The *mode*
+ and *bufsize* arguments have the same meaning as the corresponding arguments to
+ the built-in :func:`open` function. Availability: Macintosh, Unix, Windows.
+
+ .. versionchanged:: 2.3
+ When specified, the *mode* argument must now start with one of the letters
+ ``'r'``, ``'w'``, or ``'a'``, otherwise a :exc:`ValueError` is raised.
+
+ .. versionchanged:: 2.5
+ On Unix, when the *mode* argument starts with ``'a'``, the *O_APPEND* flag is
+ set on the file descriptor (which the :cfunc:`fdopen` implementation already
+ does on most platforms).
+
+
+.. function:: popen(command[, mode[, bufsize]])
+
+ Open a pipe to or from *command*. 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 *bufsize* argument has the same meaning as
+ the corresponding argument to the built-in :func:`open` function. The exit
+ status of the command (encoded in the format specified for :func:`wait`) is
+ available as the return value of the :meth:`close` method of the file object,
+ except that when the exit status is zero (termination without errors), ``None``
+ is returned. Availability: Macintosh, Unix, Windows.
+
+ .. deprecated:: 2.6
+ This function is obsolete. Use the :mod:`subprocess` module.
+
+ .. versionchanged:: 2.0
+ This function worked unreliably under Windows in earlier versions of Python.
+ This was due to the use of the :cfunc:`_popen` function from the libraries
+ provided with Windows. Newer versions of Python do not use the broken
+ implementation from the Windows libraries.
+
+
+.. function:: tmpfile()
+
+ Return a new file object opened in update mode (``w+b``). The file has no
+ directory entries associated with it and will be automatically deleted once
+ there are no file descriptors for the file. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. _os-fd-ops:
+
+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.
+
+
+.. function:: close(fd)
+
+ Close file descriptor *fd*. Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ This function is intended for low-level I/O and must be applied to a file
+ descriptor as returned by :func:`open` or :func:`pipe`. To close a "file
+ object" returned by the built-in function :func:`open` or by :func:`popen` or
+ :func:`fdopen`, use its :meth:`close` method.
+
+
+.. function:: dup(fd)
+
+ Return a duplicate of file descriptor *fd*. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: dup2(fd, fd2)
+
+ Duplicate file descriptor *fd* to *fd2*, closing the latter first if necessary.
+ Availability: Macintosh, Unix, Windows.
+
+
+.. function:: fdatasync(fd)
+
+ Force write of file with filedescriptor *fd* to disk. Does not force update of
+ metadata. Availability: Unix.
+
+
+.. function:: 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.
+ Availability: Macintosh, Unix.
+
+ If *name* is a string and is not known, :exc:`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 :exc:`OSError` is raised with
+ :const:`errno.EINVAL` for the error number.
+
+
+.. function:: fstat(fd)
+
+ Return status for file descriptor *fd*, like :func:`stat`. Availability:
+ Macintosh, Unix, Windows.
+
+
+.. function:: fstatvfs(fd)
+
+ Return information about the filesystem containing the file associated with file
+ descriptor *fd*, like :func:`statvfs`. Availability: Unix.
+
+
+.. function:: fsync(fd)
+
+ Force write of file with filedescriptor *fd* to disk. On Unix, this calls the
+ native :cfunc:`fsync` function; on Windows, the MS :cfunc:`_commit` function.
+
+ If you're starting with a Python file object *f*, first do ``f.flush()``, and
+ then do ``os.fsync(f.fileno())``, to ensure that all internal buffers associated
+ with *f* are written to disk. Availability: Macintosh, Unix, and Windows
+ starting in 2.2.3.
+
+
+.. function:: ftruncate(fd, length)
+
+ Truncate the file corresponding to file descriptor *fd*, so that it is at most
+ *length* bytes in size. Availability: Macintosh, Unix.
+
+
+.. function:: isatty(fd)
+
+ Return ``True`` if the file descriptor *fd* is open and connected to a
+ tty(-like) device, else ``False``. Availability: Macintosh, Unix.
+
+
+.. function:: lseek(fd, pos, how)
+
+ Set the current position of file descriptor *fd* to position *pos*, modified by
+ *how*: ``0`` to set the position relative to the beginning of the file; ``1`` to
+ set it relative to the current position; ``2`` to set it relative to the end of
+ the file. Availability: Macintosh, Unix, Windows.
+
+
+.. function:: open(file, flags[, mode])
+
+ Open the file *file* and set various flags according to *flags* and possibly its
+ mode according to *mode*. The default *mode* is ``0777`` (octal), and the
+ current umask value is first masked out. Return the file descriptor for the
+ newly opened file. Availability: Macintosh, Unix, Windows.
+
+ For a description of the flag and mode values, see the C run-time documentation;
+ flag constants (like :const:`O_RDONLY` and :const:`O_WRONLY`) are defined in
+ this module too (see below).
+
+ .. note::
+
+ This function is intended for low-level I/O. For normal usage, use the built-in
+ function :func:`open`, which returns a "file object" with :meth:`read` and
+ :meth:`write` methods (and many more). To wrap a file descriptor in a "file
+ object", use :func:`fdopen`.
+
+
+.. function:: openpty()
+
+ .. index:: module: pty
+
+ Open a new pseudo-terminal pair. Return a pair of file descriptors ``(master,
+ slave)`` for the pty and the tty, respectively. For a (slightly) more portable
+ approach, use the :mod:`pty` module. Availability: Macintosh, Some flavors of
+ Unix.
+
+
+.. function:: pipe()
+
+ Create a pipe. Return a pair of file descriptors ``(r, w)`` usable for reading
+ and writing, respectively. Availability: Macintosh, Unix, Windows.
+
+
+.. function:: read(fd, n)
+
+ Read at most *n* bytes from file descriptor *fd*. Return a string containing the
+ bytes read. If the end of the file referred to by *fd* has been reached, an
+ empty string is returned. Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ This function is intended for low-level I/O and must be applied to a file
+ descriptor as returned by :func:`open` or :func:`pipe`. To read a "file object"
+ returned by the built-in function :func:`open` or by :func:`popen` or
+ :func:`fdopen`, or ``sys.stdin``, use its :meth:`read` or :meth:`readline`
+ methods.
+
+
+.. function:: tcgetpgrp(fd)
+
+ Return the process group associated with the terminal given by *fd* (an open
+ file descriptor as returned by :func:`open`). Availability: Macintosh, Unix.
+
+
+.. function:: tcsetpgrp(fd, pg)
+
+ Set the process group associated with the terminal given by *fd* (an open file
+ descriptor as returned by :func:`open`) to *pg*. Availability: Macintosh, Unix.
+
+
+.. function:: ttyname(fd)
+
+ Return a string which specifies the terminal device associated with
+ file-descriptor *fd*. If *fd* is not associated with a terminal device, an
+ exception is raised. Availability:Macintosh, Unix.
+
+
+.. function:: write(fd, str)
+
+ Write the string *str* to file descriptor *fd*. Return the number of bytes
+ actually written. Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ This function is intended for low-level I/O and must be applied to a file
+ descriptor as returned by :func:`open` or :func:`pipe`. To write a "file
+ object" returned by the built-in function :func:`open` or by :func:`popen` or
+ :func:`fdopen`, or ``sys.stdout`` or ``sys.stderr``, use its :meth:`write`
+ method.
+
+The following data items are available for use in constructing the *flags*
+parameter to the :func:`open` function. Some items will not be available on all
+platforms. For descriptions of their availability and use, consult
+:manpage:`open(2)`.
+
+
+.. data:: O_RDONLY
+ O_WRONLY
+ O_RDWR
+ O_APPEND
+ O_CREAT
+ O_EXCL
+ O_TRUNC
+
+ Options for the *flag* argument to the :func:`open` function. These can be
+ bit-wise OR'd together. Availability: Macintosh, Unix, Windows.
+
+
+.. data:: O_DSYNC
+ O_RSYNC
+ O_SYNC
+ O_NDELAY
+ O_NONBLOCK
+ O_NOCTTY
+ O_SHLOCK
+ O_EXLOCK
+
+ More options for the *flag* argument to the :func:`open` function. Availability:
+ Macintosh, Unix.
+
+
+.. data:: O_BINARY
+
+ Option for the *flag* argument to the :func:`open` function. This can be
+ bit-wise OR'd together with those listed above. Availability: Windows.
+
+ .. % XXX need to check on the availability of this one.
+
+
+.. data:: O_NOINHERIT
+ O_SHORT_LIVED
+ O_TEMPORARY
+ O_RANDOM
+ O_SEQUENTIAL
+ O_TEXT
+
+ Options for the *flag* argument to the :func:`open` function. These can be
+ bit-wise OR'd together. Availability: Windows.
+
+
+.. data:: SEEK_SET
+ SEEK_CUR
+ SEEK_END
+
+ Parameters to the :func:`lseek` function. Their values are 0, 1, and 2,
+ respectively. Availability: Windows, Macintosh, Unix.
+
+ .. versionadded:: 2.5
+
+
+.. _os-file-dir:
+
+Files and Directories
+---------------------
+
+
+.. function:: access(path, mode)
+
+ 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 :const:`F_OK` to test the existence of *path*, or it
+ can be the inclusive OR of one or more of :const:`R_OK`, :const:`W_OK`, and
+ :const:`X_OK` to test permissions. Return :const:`True` if access is allowed,
+ :const:`False` if not. See the Unix man page :manpage:`access(2)` for more
+ information. Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ Using :func:`access` to check if a user is authorized to e.g. open a file before
+ actually doing so using :func:`open` creates a security hole, because the user
+ might exploit the short time interval between checking and opening the file to
+ manipulate it.
+
+ .. note::
+
+ I/O operations may fail even when :func:`access` indicates that they would
+ succeed, particularly for operations on network filesystems which may have
+ permissions semantics beyond the usual POSIX permission-bit model.
+
+
+.. data:: F_OK
+
+ Value to pass as the *mode* parameter of :func:`access` to test the existence of
+ *path*.
+
+
+.. data:: R_OK
+
+ Value to include in the *mode* parameter of :func:`access` to test the
+ readability of *path*.
+
+
+.. data:: W_OK
+
+ Value to include in the *mode* parameter of :func:`access` to test the
+ writability of *path*.
+
+
+.. data:: X_OK
+
+ Value to include in the *mode* parameter of :func:`access` to determine if
+ *path* can be executed.
+
+
+.. function:: chdir(path)
+
+ .. index:: single: directory; changing
+
+ Change the current working directory to *path*. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: 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. Availability: Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: getcwd()
+
+ Return a string representing the current working directory. Availability:
+ Macintosh, Unix, Windows.
+
+
+.. function:: getcwdu()
+
+ Return a Unicode object representing the current working directory.
+ Availability: Macintosh, Unix, Windows.
+
+ .. versionadded:: 2.3
+
+
+.. function:: chflags(path, flags)
+
+ Set the flags of *path* to the numeric *flags*. *flags* may take a combination
+ (bitwise OR) of the following values (as defined in the :mod:`stat` module):
+
+ * ``UF_NODUMP``
+ * ``UF_IMMUTABLE``
+ * ``UF_APPEND``
+ * ``UF_OPAQUE``
+ * ``UF_NOUNLINK``
+ * ``SF_ARCHIVED``
+ * ``SF_IMMUTABLE``
+ * ``SF_APPEND``
+ * ``SF_NOUNLINK``
+ * ``SF_SNAPSHOT``
+
+ Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.6
+
+
+.. function:: chroot(path)
+
+ Change the root directory of the current process to *path*. Availability:
+ Macintosh, Unix.
+
+ .. versionadded:: 2.2
+
+
+.. function:: chmod(path, mode)
+
+ Change the mode of *path* to the numeric *mode*. *mode* may take one of the
+ following values (as defined in the :mod:`stat` module) or bitwise or-ed
+ 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``
+
+ Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ Although Windows supports :func:`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.
+
+
+.. function:: chown(path, uid, gid)
+
+ 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. Availability: Macintosh, Unix.
+
+
+.. function:: lchflags(path, flags)
+
+ Set the flags of *path* to the numeric *flags*, like :func:`chflags`, but do not
+ follow symbolic links. Availability: Unix.
+
+ .. versionadded:: 2.6
+
+
+.. function:: 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. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: link(src, dst)
+
+ Create a hard link pointing to *src* named *dst*. Availability: Macintosh, Unix.
+
+
+.. function:: listdir(path)
+
+ Return a list containing the names of the entries in the directory. The list is
+ in arbitrary order. It does not include the special entries ``'.'`` and
+ ``'..'`` even if they are present in the directory. Availability: Macintosh,
+ Unix, Windows.
+
+ .. versionchanged:: 2.3
+ On Windows NT/2k/XP and Unix, if *path* is a Unicode object, the result will be
+ a list of Unicode objects.
+
+
+.. function:: lstat(path)
+
+ Like :func:`stat`, but do not follow symbolic links. Availability: Macintosh,
+ Unix.
+
+
+.. function:: mkfifo(path[, mode])
+
+ Create a FIFO (a named pipe) named *path* with numeric mode *mode*. The default
+ *mode* is ``0666`` (octal). The current umask value is first masked out from
+ the mode. Availability: Macintosh, Unix.
+
+ FIFOs are pipes that can be accessed like regular files. FIFOs exist until they
+ are deleted (for example with :func:`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 :func:`mkfifo`
+ doesn't open the FIFO --- it just creates the rendezvous point.
+
+
+.. function:: mknod(filename[, mode=0600, device])
+
+ Create a filesystem node (file, device special file or named pipe) named
+ *filename*. *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 :mod:`stat`).
+ For ``stat.S_IFCHR`` and
+ ``stat.S_IFBLK``, *device* defines the newly created device special file (probably using
+ :func:`os.makedev`), otherwise it is ignored.
+
+ .. versionadded:: 2.3
+
+
+.. function:: major(device)
+
+ Extracts the device major number from a raw device number (usually the
+ :attr:`st_dev` or :attr:`st_rdev` field from :ctype:`stat`).
+
+ .. versionadded:: 2.3
+
+
+.. function:: minor(device)
+
+ Extracts the device minor number from a raw device number (usually the
+ :attr:`st_dev` or :attr:`st_rdev` field from :ctype:`stat`).
+
+ .. versionadded:: 2.3
+
+
+.. function:: makedev(major, minor)
+
+ Composes a raw device number from the major and minor device numbers.
+
+ .. versionadded:: 2.3
+
+
+.. function:: mkdir(path[, mode])
+
+ Create a directory named *path* with numeric mode *mode*. The default *mode* is
+ ``0777`` (octal). On some systems, *mode* is ignored. Where it is used, the
+ current umask value is first masked out. Availability: Macintosh, Unix, Windows.
+
+
+.. function:: makedirs(path[, mode])
+
+ .. index::
+ single: directory; creating
+ single: UNC paths; and os.makedirs()
+
+ Recursive directory creation function. Like :func:`mkdir`, but makes all
+ intermediate-level directories needed to contain the leaf directory. Throws an
+ :exc:`error` exception if the leaf directory already exists or cannot be
+ created. The default *mode* is ``0777`` (octal). On some systems, *mode* is
+ ignored. Where it is used, the current umask value is first masked out.
+
+ .. note::
+
+ :func:`makedirs` will become confused if the path elements to create include
+ *os.pardir*.
+
+ .. versionadded:: 1.5.2
+
+ .. versionchanged:: 2.3
+ This function now handles UNC paths correctly.
+
+
+.. function:: 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.
+ Availability: Macintosh, Unix.
+
+ If *name* is a string and is not known, :exc:`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 :exc:`OSError` is raised with
+ :const:`errno.EINVAL` for the error number.
+
+
+.. data:: pathconf_names
+
+ Dictionary mapping names accepted by :func:`pathconf` and :func:`fpathconf` to
+ the integer values defined for those names by the host operating system. This
+ can be used to determine the set of names known to the system. Availability:
+ Macintosh, Unix.
+
+
+.. function:: readlink(path)
+
+ 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)``.
+
+ .. versionchanged:: 2.6
+ If the *path* is a Unicode object the result will also be a Unicode object.
+
+ Availability: Macintosh, Unix.
+
+
+.. function:: remove(path)
+
+ Remove the file *path*. If *path* is a directory, :exc:`OSError` is raised; see
+ :func:`rmdir` below to remove a directory. This is identical to the
+ :func:`unlink` function documented below. 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. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: removedirs(path)
+
+ .. index:: single: directory; deleting
+
+ Removes directories recursively. Works like :func:`rmdir` except that, if the
+ leaf directory is successfully removed, :func:`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 :exc:`OSError` if the leaf directory could not be
+ successfully removed.
+
+ .. versionadded:: 1.5.2
+
+
+.. function:: rename(src, dst)
+
+ Rename the file or directory *src* to *dst*. If *dst* is a directory,
+ :exc:`OSError` will be raised. On Unix, if *dst* exists and is a file, it will
+ be removed 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). On
+ Windows, if *dst* already exists, :exc:`OSError` will be raised even if it is a
+ file; there may be no way to implement an atomic rename when *dst* names an
+ existing file. Availability: Macintosh, Unix, Windows.
+
+
+.. function:: renames(old, new)
+
+ Recursive directory or file renaming function. Works like :func:`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 :func:`removedirs`.
+
+ .. versionadded:: 1.5.2
+
+ .. note::
+
+ This function can fail with the new directory structure made if you lack
+ permissions needed to remove the leaf directory or file.
+
+
+.. function:: rmdir(path)
+
+ Remove the directory *path*. Availability: Macintosh, Unix, Windows.
+
+
+.. function:: stat(path)
+
+ Perform a :cfunc:`stat` system call on the given path. The return value is an
+ object whose attributes correspond to the members of the :ctype:`stat`
+ structure, namely: :attr:`st_mode` (protection bits), :attr:`st_ino` (inode
+ number), :attr:`st_dev` (device), :attr:`st_nlink` (number of hard links),
+ :attr:`st_uid` (user ID of owner), :attr:`st_gid` (group ID of owner),
+ :attr:`st_size` (size of file, in bytes), :attr:`st_atime` (time of most recent
+ access), :attr:`st_mtime` (time of most recent content modification),
+ :attr:`st_ctime` (platform dependent; time of most recent metadata change on
+ Unix, or the time of creation on Windows)::
+
+ >>> import os
+ >>> statinfo = os.stat('somefile.txt')
+ >>> statinfo
+ (33188, 422511L, 769L, 1, 1032, 100, 926L, 1105022698,1105022732, 1105022732)
+ >>> statinfo.st_size
+ 926L
+ >>>
+
+ .. versionchanged:: 2.3
+ If :func:`stat_float_times` returns true, the time values are floats, measuring
+ seconds. Fractions of a second may be reported if the system supports that. On
+ Mac OS, the times are always floats. See :func:`stat_float_times` for further
+ discussion.
+
+ On some Unix systems (such as Linux), the following attributes may also be
+ available: :attr:`st_blocks` (number of blocks allocated for file),
+ :attr:`st_blksize` (filesystem blocksize), :attr:`st_rdev` (type of device if an
+ inode device). :attr:`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): :attr:`st_gen`
+ (file generation number), :attr:`st_birthtime` (time of file creation).
+
+ On Mac OS systems, the following attributes may also be available:
+ :attr:`st_rsize`, :attr:`st_creator`, :attr:`st_type`.
+
+ On RISCOS systems, the following attributes are also available: :attr:`st_ftype`
+ (file type), :attr:`st_attrs` (attributes), :attr:`st_obtype` (object type).
+
+ .. index:: module: stat
+
+ For backward compatibility, the return value of :func:`stat` is also accessible
+ as a tuple of at least 10 integers giving the most important (and portable)
+ members of the :ctype:`stat` structure, in the order :attr:`st_mode`,
+ :attr:`st_ino`, :attr:`st_dev`, :attr:`st_nlink`, :attr:`st_uid`,
+ :attr:`st_gid`, :attr:`st_size`, :attr:`st_atime`, :attr:`st_mtime`,
+ :attr:`st_ctime`. More items may be added at the end by some implementations.
+ The standard module :mod:`stat` defines functions and constants that are useful
+ for extracting information from a :ctype:`stat` structure. (On Windows, some
+ items are filled with dummy values.)
+
+ .. note::
+
+ The exact meaning and resolution of the :attr:`st_atime`, :attr:`st_mtime`, and
+ :attr:`st_ctime` members depends on the operating system and the file system.
+ For example, on Windows systems using the FAT or FAT32 file systems,
+ :attr:`st_mtime` has 2-second resolution, and :attr:`st_atime` has only 1-day
+ resolution. See your operating system documentation for details.
+
+ Availability: Macintosh, Unix, Windows.
+
+ .. versionchanged:: 2.2
+ Added access to values as attributes of the returned object.
+
+ .. versionchanged:: 2.5
+ Added st_gen, st_birthtime.
+
+
+.. function:: stat_float_times([newvalue])
+
+ Determine whether :class:`stat_result` represents time stamps as float objects.
+ If *newvalue* is ``True``, future calls to :func:`stat` return floats, if it is
+ ``False``, future calls return ints. If *newvalue* is omitted, return the
+ current setting.
+
+ For compatibility with older Python versions, accessing :class:`stat_result` as
+ a tuple always returns integers.
+
+ .. versionchanged:: 2.5
+ Python now returns float values by default. Applications which do not work
+ correctly with floating point time stamps can use this function to restore the
+ old behaviour.
+
+ The resolution of the timestamps (that is the smallest possible fraction)
+ depends on the system. Some systems only support second resolution; on these
+ systems, the fraction will always be zero.
+
+ It is recommended that this setting is only changed at program startup time in
+ the *__main__* module; libraries should never change this setting. If an
+ application uses a library that works incorrectly if floating point time stamps
+ are processed, this application should turn the feature off until the library
+ has been corrected.
+
+
+.. function:: statvfs(path)
+
+ Perform a :cfunc:`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 :ctype:`statvfs` structure, namely:
+ :attr:`f_bsize`, :attr:`f_frsize`, :attr:`f_blocks`, :attr:`f_bfree`,
+ :attr:`f_bavail`, :attr:`f_files`, :attr:`f_ffree`, :attr:`f_favail`,
+ :attr:`f_flag`, :attr:`f_namemax`. Availability: Unix.
+
+ .. index:: module: statvfs
+
+ For backward compatibility, the return value is also accessible as a tuple whose
+ values correspond to the attributes, in the order given above. The standard
+ module :mod:`statvfs` defines constants that are useful for extracting
+ information from a :ctype:`statvfs` structure when accessing it as a sequence;
+ this remains useful when writing code that needs to work with versions of Python
+ that don't support accessing the fields as attributes.
+
+ .. versionchanged:: 2.2
+ Added access to values as attributes of the returned object.
+
+
+.. function:: symlink(src, dst)
+
+ Create a symbolic link pointing to *src* named *dst*. Availability: Unix.
+
+
+.. function:: tempnam([dir[, prefix]])
+
+ Return a unique path name that is reasonable for creating a temporary file.
+ This will be an absolute path that names a potential directory entry in the
+ directory *dir* or a common location for temporary files if *dir* is omitted or
+ ``None``. If given and not ``None``, *prefix* is used to provide a short prefix
+ to the filename. Applications are responsible for properly creating and
+ managing files created using paths returned by :func:`tempnam`; no automatic
+ cleanup is provided. On Unix, the environment variable :envvar:`TMPDIR`
+ overrides *dir*, while on Windows the :envvar:`TMP` is used. The specific
+ behavior of this function depends on the C library implementation; some aspects
+ are underspecified in system documentation.
+
+ .. warning::
+
+ Use of :func:`tempnam` is vulnerable to symlink attacks; consider using
+ :func:`tmpfile` (section :ref:`os-newstreams`) instead.
+
+ Availability: Macintosh, Unix, Windows.
+
+
+.. function:: tmpnam()
+
+ Return a unique path name that is reasonable for creating a temporary file.
+ This will be an absolute path that names a potential directory entry in a common
+ location for temporary files. Applications are responsible for properly
+ creating and managing files created using paths returned by :func:`tmpnam`; no
+ automatic cleanup is provided.
+
+ .. warning::
+
+ Use of :func:`tmpnam` is vulnerable to symlink attacks; consider using
+ :func:`tmpfile` (section :ref:`os-newstreams`) instead.
+
+ Availability: Unix, Windows. This function probably shouldn't be used on
+ Windows, though: Microsoft's implementation of :func:`tmpnam` always creates a
+ name in the root directory of the current drive, and that's generally a poor
+ location for a temp file (depending on privileges, you may not even be able to
+ open a file using this name).
+
+
+.. data:: TMP_MAX
+
+ The maximum number of unique names that :func:`tmpnam` will generate before
+ reusing names.
+
+
+.. function:: unlink(path)
+
+ Remove the file *path*. This is the same function as :func:`remove`; the
+ :func:`unlink` name is its traditional Unix name. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: utime(path, times)
+
+ Set the access and modified times of the file specified by *path*. If *times* is
+ ``None``, then the file's access and modified times are set to the current time.
+ Otherwise, *times* must be a 2-tuple of numbers, of the form ``(atime, mtime)``
+ which is used to set the access and modified times, respectively. Whether a
+ directory can be given for *path* depends on whether the operating system
+ implements directories as files (for example, Windows does not). Note that the
+ exact times you set here may not be returned by a subsequent :func:`stat` call,
+ depending on the resolution with which your operating system records access and
+ modification times; see :func:`stat`.
+
+ .. versionchanged:: 2.0
+ Added support for ``None`` for *times*.
+
+ Availability: Macintosh, Unix, Windows.
+
+
+.. function:: walk(top[, topdown=True [, onerror=None[, followlinks=False]]])
+
+ .. index::
+ single: directory; walking
+ single: directory; traversal
+
+ :func:`walk` generates 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).
+
+ When *topdown* is true, the caller can modify the *dirnames* list in-place
+ (perhaps using :keyword:`del` or slice assignment), and :func:`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
+ :func:`walk` about directories the caller creates or renames before it resumes
+ :func:`walk` again. Modifying *dirnames* when *topdown* is false is
+ ineffective, because in bottom-up mode the directories in *dirnames* are
+ generated before *dirpath* itself is generated.
+
+ By default errors from the ``os.listdir()`` call are ignored. If optional
+ argument *onerror* is specified, it should be a function; it will be called with
+ one argument, an :exc:`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, :func:`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.
+
+ .. versionadded:: 2.6
+ The *followlinks* parameter.
+
+ .. note::
+
+ Be aware that setting *followlinks* to true can lead to infinite recursion if a
+ link points to a parent directory of itself. :func:`walk` does not keep track of
+ the directories it visited already.
+
+ .. note::
+
+ If you pass a relative pathname, don't change the current working directory
+ between resumptions of :func:`walk`. :func:`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",
+ print sum(getsize(join(root, name)) for name in files),
+ 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: :func:`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))
+
+ .. versionadded:: 2.3
+
+
+.. _os-process:
+
+Process Management
+------------------
+
+These functions may be used to create and manage processes.
+
+The various :func:`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 :cfunc:`main`. For example, ``os.execv('/bin/echo',
+['foo', 'bar'])`` will only print ``bar`` on standard output; ``foo`` will seem
+to be ignored.
+
+
+.. function:: abort()
+
+ Generate a :const:`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 programs which use :func:`signal.signal`
+ to register a handler for :const:`SIGABRT` will behave differently.
+ Availability: Macintosh, Unix, Windows.
+
+
+.. function:: execl(path, arg0, arg1, ...)
+ execle(path, arg0, arg1, ..., env)
+ execlp(file, arg0, arg1, ...)
+ execlpe(file, arg0, arg1, ..., env)
+ execv(path, args)
+ execve(path, args, env)
+ execvp(file, args)
+ 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
+ :exc:`OSError` exceptions.
+
+ The ``'l'`` and ``'v'`` variants of the :func:`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 :func:`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 (:func:`execlp`,
+ :func:`execlpe`, :func:`execvp`, and :func:`execvpe`) will use the
+ :envvar:`PATH` environment variable to locate the program *file*. When the
+ environment is being replaced (using one of the :func:`exec\*e` variants,
+ discussed in the next paragraph), the new environment is used as the source of
+ the :envvar:`PATH` variable. The other variants, :func:`execl`, :func:`execle`,
+ :func:`execv`, and :func:`execve`, will not use the :envvar:`PATH` variable to
+ locate the executable; *path* must contain an appropriate absolute or relative
+ path.
+
+ For :func:`execle`, :func:`execlpe`, :func:`execve`, and :func:`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; the :func:`execl`,
+ :func:`execlp`, :func:`execv`, and :func:`execvp` all cause the new process to
+ inherit the environment of the current process. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: _exit(n)
+
+ Exit to the system with status *n*, without calling cleanup handlers, flushing
+ stdio buffers, etc. Availability: Macintosh, Unix, Windows.
+
+ .. note::
+
+ The standard way to exit is ``sys.exit(n)``. :func:`_exit` should normally only
+ be used in the child process after a :func:`fork`.
+
+The following exit codes are a defined, and can be used with :func:`_exit`,
+although they are not required. These are typically used for system programs
+written in Python, such as a mail server's external command delivery program.
+
+.. note::
+
+ Some of these may not be available on all Unix platforms, since there is some
+ variation. These constants are defined where they are defined by the underlying
+ platform.
+
+
+.. data:: EX_OK
+
+ Exit code that means no error occurred. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_USAGE
+
+ Exit code that means the command was used incorrectly, such as when the wrong
+ number of arguments are given. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_DATAERR
+
+ Exit code that means the input data was incorrect. Availability: Macintosh,
+ Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_NOINPUT
+
+ Exit code that means an input file did not exist or was not readable.
+ Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_NOUSER
+
+ Exit code that means a specified user did not exist. Availability: Macintosh,
+ Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_NOHOST
+
+ Exit code that means a specified host did not exist. Availability: Macintosh,
+ Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_UNAVAILABLE
+
+ Exit code that means that a required service is unavailable. Availability:
+ Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_SOFTWARE
+
+ Exit code that means an internal software error was detected. Availability:
+ Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_OSERR
+
+ Exit code that means an operating system error was detected, such as the
+ inability to fork or create a pipe. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_OSFILE
+
+ Exit code that means some system file did not exist, could not be opened, or had
+ some other kind of error. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_CANTCREAT
+
+ Exit code that means a user specified output file could not be created.
+ Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_IOERR
+
+ Exit code that means that an error occurred while doing I/O on some file.
+ Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_TEMPFAIL
+
+ Exit code that means a temporary failure occurred. This indicates something
+ that may not really be an error, such as a network connection that couldn't be
+ made during a retryable operation. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_PROTOCOL
+
+ Exit code that means that a protocol exchange was illegal, invalid, or not
+ understood. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_NOPERM
+
+ Exit code that means that there were insufficient permissions to perform the
+ operation (but not intended for file system problems). Availability: Macintosh,
+ Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_CONFIG
+
+ Exit code that means that some kind of configuration error occurred.
+ Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. data:: EX_NOTFOUND
+
+ Exit code that means something like "an entry was not found". Availability:
+ Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: fork()
+
+ Fork a child process. Return ``0`` in the child, the child's process id in the
+ parent. Availability: Macintosh, Unix.
+
+
+.. function:: 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
+ :mod:`pty` module. Availability: Macintosh, Some flavors of Unix.
+
+
+.. function:: kill(pid, sig)
+
+ .. index::
+ single: process; killing
+ single: process; signalling
+
+ Send signal *sig* to the process *pid*. Constants for the specific signals
+ available on the host platform are defined in the :mod:`signal` module.
+ Availability: Macintosh, Unix.
+
+
+.. function:: killpg(pgid, sig)
+
+ .. index::
+ single: process; killing
+ single: process; signalling
+
+ Send the signal *sig* to the process group *pgid*. Availability: Macintosh,
+ Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: nice(increment)
+
+ Add *increment* to the process's "niceness". Return the new niceness.
+ Availability: Macintosh, Unix.
+
+
+.. function:: plock(op)
+
+ Lock program segments into memory. The value of *op* (defined in
+ ``<sys/lock.h>``) determines which segments are locked. Availability: Macintosh,
+ Unix.
+
+
+.. function:: popen(...)
+ :noindex:
+
+ Run child processes, returning opened pipes for communications. These functions
+ are described in section :ref:`os-newstreams`.
+
+
+.. function:: spawnl(mode, path, ...)
+ spawnle(mode, path, ..., env)
+ spawnlp(mode, file, ...)
+ spawnlpe(mode, file, ..., env)
+ spawnv(mode, path, args)
+ spawnve(mode, path, args, env)
+ spawnvp(mode, file, args)
+ spawnvpe(mode, file, args, env)
+
+ Execute the program *path* in a new process.
+
+ (Note that the :mod:`subprocess` module provides more powerful facilities for
+ spawning new processes and retrieving their results; using that module is
+ preferable to using these functions.)
+
+ If *mode* is :const:`P_NOWAIT`, this function returns the process ID of the new
+ process; if *mode* is :const:`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 :func:`waitpid` function.
+
+ The ``'l'`` and ``'v'`` variants of the :func:`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
+ :func:`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 (:func:`spawnlp`,
+ :func:`spawnlpe`, :func:`spawnvp`, and :func:`spawnvpe`) will use the
+ :envvar:`PATH` environment variable to locate the program *file*. When the
+ environment is being replaced (using one of the :func:`spawn\*e` variants,
+ discussed in the next paragraph), the new environment is used as the source of
+ the :envvar:`PATH` variable. The other variants, :func:`spawnl`,
+ :func:`spawnle`, :func:`spawnv`, and :func:`spawnve`, will not use the
+ :envvar:`PATH` variable to locate the executable; *path* must contain an
+ appropriate absolute or relative path.
+
+ For :func:`spawnle`, :func:`spawnlpe`, :func:`spawnve`, and :func:`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; the
+ :func:`spawnl`, :func:`spawnlp`, :func:`spawnv`, and :func:`spawnvp` all cause
+ the new process to inherit the environment of the current process.
+
+ As an example, the following calls to :func:`spawnlp` and :func:`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. :func:`spawnlp`, :func:`spawnlpe`, :func:`spawnvp`
+ and :func:`spawnvpe` are not available on Windows.
+
+ .. versionadded:: 1.6
+
+
+.. data:: P_NOWAIT
+ P_NOWAITO
+
+ Possible values for the *mode* parameter to the :func:`spawn\*` family of
+ functions. If either of these values is given, the :func:`spawn\*` functions
+ will return as soon as the new process has been created, with the process ID as
+ the return value. Availability: Macintosh, Unix, Windows.
+
+ .. versionadded:: 1.6
+
+
+.. data:: P_WAIT
+
+ Possible value for the *mode* parameter to the :func:`spawn\*` family of
+ functions. If this is given as *mode*, the :func:`spawn\*` functions will not
+ return until the new process has run to completion and will return the exit code
+ of the process the run is successful, or ``-signal`` if a signal kills the
+ process. Availability: Macintosh, Unix, Windows.
+
+ .. versionadded:: 1.6
+
+
+.. data:: P_DETACH
+ P_OVERLAY
+
+ Possible values for the *mode* parameter to the :func:`spawn\*` family of
+ functions. These are less portable than those listed above. :const:`P_DETACH`
+ is similar to :const:`P_NOWAIT`, but the new process is detached from the
+ console of the calling process. If :const:`P_OVERLAY` is used, the current
+ process will be replaced; the :func:`spawn\*` function will not return.
+ Availability: Windows.
+
+ .. versionadded:: 1.6
+
+
+.. function:: 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
+ :program:`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).
+
+ :func:`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 :cfunc:`ShellExecute` function
+ doesn't work if it is. Use the :func:`os.path.normpath` function to ensure that
+ the path is properly encoded for Win32. Availability: Windows.
+
+ .. versionadded:: 2.0
+
+ .. versionadded:: 2.5
+ The *operation* parameter.
+
+
+.. function:: system(command)
+
+ Execute the command (a string) in a subshell. This is implemented by calling
+ the Standard C function :cfunc:`system`, and has the same limitations. Changes
+ to ``posix.environ``, ``sys.stdin``, etc. are not reflected in the environment
+ of the executed command.
+
+ On Unix, the return value is the exit status of the process encoded in the
+ format specified for :func:`wait`. Note that POSIX does not specify the meaning
+ of the return value of the C :cfunc:`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*, given by the Windows environment variable :envvar:`COMSPEC`: on
+ :program:`command.com` systems (Windows 95, 98 and ME) this is always ``0``; on
+ :program:`cmd.exe` systems (Windows NT, 2000 and XP) this is the exit status of
+ the command run; on systems using a non-native shell, consult your shell
+ documentation.
+
+ Availability: Macintosh, Unix, Windows.
+
+ The :mod:`subprocess` module provides more powerful facilities for spawning new
+ processes and retrieving their results; using that module is preferable to using
+ this function.
+
+
+.. function:: times()
+
+ Return a 5-tuple of floating point numbers indicating accumulated (processor or
+ other) times, in seconds. The items are: user time, system time, children's
+ user time, children's system time, and elapsed real time since a fixed point in
+ the past, in that order. See the Unix manual page :manpage:`times(2)` or the
+ corresponding Windows Platform API documentation. Availability: Macintosh, Unix,
+ Windows.
+
+
+.. function:: 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. Availability: Macintosh, Unix.
+
+
+.. function:: 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 :func:`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``, :func:`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*).
+
+ 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 :func:`spawn` functions called
+ with :const:`P_NOWAIT` return suitable process handles.
+
+
+.. function:: wait3([options])
+
+ Similar to :func:`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 :mod:`resource`.\
+ :func:`getrusage` for details on resource usage information. The option
+ argument is the same as that provided to :func:`waitpid` and :func:`wait4`.
+ Availability: Unix.
+
+ .. versionadded:: 2.5
+
+
+.. function:: wait4(pid, options)
+
+ Similar to :func:`waitpid`, except a 3-element tuple, containing the child's
+ process id, exit status indication, and resource usage information is returned.
+ Refer to :mod:`resource`.\ :func:`getrusage` for details on resource usage
+ information. The arguments to :func:`wait4` are the same as those provided to
+ :func:`waitpid`. Availability: Unix.
+
+ .. versionadded:: 2.5
+
+
+.. data:: WNOHANG
+
+ The option for :func:`waitpid` to return immediately if no child process status
+ is available immediately. The function returns ``(0, 0)`` in this case.
+ Availability: Macintosh, Unix.
+
+
+.. data:: WCONTINUED
+
+ This option causes child processes to be reported if they have been continued
+ from a job control stop since their status was last reported. Availability: Some
+ Unix systems.
+
+ .. versionadded:: 2.3
+
+
+.. data:: WUNTRACED
+
+ This option causes child processes to be reported if they have been stopped but
+ their current state has not been reported since they were stopped. Availability:
+ Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+The following functions take a process status code as returned by
+:func:`system`, :func:`wait`, or :func:`waitpid` as a parameter. They may be
+used to determine the disposition of a process.
+
+
+.. function:: WCOREDUMP(status)
+
+ Returns ``True`` if a core dump was generated for the process, otherwise it
+ returns ``False``. Availability: Macintosh, Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: WIFCONTINUED(status)
+
+ Returns ``True`` if the process has been continued from a job control stop,
+ otherwise it returns ``False``. Availability: Unix.
+
+ .. versionadded:: 2.3
+
+
+.. function:: WIFSTOPPED(status)
+
+ Returns ``True`` if the process has been stopped, otherwise it returns
+ ``False``. Availability: Unix.
+
+
+.. function:: WIFSIGNALED(status)
+
+ Returns ``True`` if the process exited due to a signal, otherwise it returns
+ ``False``. Availability: Macintosh, Unix.
+
+
+.. function:: WIFEXITED(status)
+
+ Returns ``True`` if the process exited using the :manpage:`exit(2)` system call,
+ otherwise it returns ``False``. Availability: Macintosh, Unix.
+
+
+.. function:: WEXITSTATUS(status)
+
+ If ``WIFEXITED(status)`` is true, return the integer parameter to the
+ :manpage:`exit(2)` system call. Otherwise, the return value is meaningless.
+ Availability: Macintosh, Unix.
+
+
+.. function:: WSTOPSIG(status)
+
+ Return the signal which caused the process to stop. Availability: Macintosh,
+ Unix.
+
+
+.. function:: WTERMSIG(status)
+
+ Return the signal which caused the process to exit. Availability: Macintosh,
+ Unix.
+
+
+.. _os-path:
+
+Miscellaneous System Information
+--------------------------------
+
+
+.. function:: 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. Availability:
+ Macintosh, Unix.
+
+ If the configuration value specified by *name* isn't defined, ``None`` is
+ returned.
+
+ If *name* is a string and is not known, :exc:`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 :exc:`OSError` is raised with
+ :const:`errno.EINVAL` for the error number.
+
+
+.. data:: confstr_names
+
+ Dictionary mapping names accepted by :func:`confstr` to the integer values
+ defined for those names by the host operating system. This can be used to
+ determine the set of names known to the system. Availability: Macintosh, Unix.
+
+
+.. function:: getloadavg()
+
+ Return the number of processes in the system run queue averaged over the last 1,
+ 5, and 15 minutes or raises :exc:`OSError` if the load average was
+ unobtainable.
+
+ .. versionadded:: 2.3
+
+
+.. function:: 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 :func:`confstr` apply here as well; the dictionary that
+ provides information on the known names is given by ``sysconf_names``.
+ Availability: Macintosh, Unix.
+
+
+.. data:: sysconf_names
+
+ Dictionary mapping names accepted by :func:`sysconf` to the integer values
+ defined for those names by the host operating system. This can be used to
+ determine the set of names known to the system. Availability: Macintosh, Unix.
+
+The follow data values are used to support path manipulation operations. These
+are defined for all platforms.
+
+Higher-level operations on pathnames are defined in the :mod:`os.path` module.
+
+
+.. data:: curdir
+
+ The constant string used by the operating system to refer to the current
+ directory. For example: ``'.'`` for POSIX or ``':'`` for Mac OS 9. Also
+ available via :mod:`os.path`.
+
+
+.. data:: pardir
+
+ The constant string used by the operating system to refer to the parent
+ directory. For example: ``'..'`` for POSIX or ``'::'`` for Mac OS 9. Also
+ available via :mod:`os.path`.
+
+
+.. data:: sep
+
+ The character used by the operating system to separate pathname components, for
+ example, ``'/'`` for POSIX or ``':'`` for Mac OS 9. Note that knowing this is
+ not sufficient to be able to parse or concatenate pathnames --- use
+ :func:`os.path.split` and :func:`os.path.join` --- but it is occasionally
+ useful. Also available via :mod:`os.path`.
+
+
+.. data:: 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
+ :mod:`os.path`.
+
+
+.. data:: extsep
+
+ The character which separates the base filename from the extension; for example,
+ the ``'.'`` in :file:`os.py`. Also available via :mod:`os.path`.
+
+ .. versionadded:: 2.2
+
+
+.. data:: pathsep
+
+ The character conventionally used by the operating system to separate search
+ path components (as in :envvar:`PATH`), such as ``':'`` for POSIX or ``';'`` for
+ Windows. Also available via :mod:`os.path`.
+
+
+.. data:: defpath
+
+ The default search path used by :func:`exec\*p\*` and :func:`spawn\*p\*` if the
+ environment doesn't have a ``'PATH'`` key. Also available via :mod:`os.path`.
+
+
+.. data:: 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
+ ``'\r'`` for Mac OS, 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.
+
+
+.. data:: devnull
+
+ The file path of the null device. For example: ``'/dev/null'`` for POSIX or
+ ``'Dev:Nul'`` for Mac OS 9. Also available via :mod:`os.path`.
+
+ .. versionadded:: 2.4
+
+
+.. _os-miscfunc:
+
+Miscellaneous Functions
+-----------------------
+
+
+.. function:: urandom(n)
+
+ Return a string of *n* 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 a UNIX-like
+ system this will query /dev/urandom, and on Windows it will use CryptGenRandom.
+ If a randomness source is not found, :exc:`NotImplementedError` will be raised.
+
+ .. versionadded:: 2.4
+