:mod:`os` --- Miscellaneous operating system interfaces
=======================================================
.. module:: os
:synopsis: Miscellaneous operating system interfaces.
This module provides a portable way of using operating system dependent
functionality. If you just want to read or write a file see :func:`open`, if
you want to manipulate paths, see the :mod:`os.path` module, and if you want to
read all the lines in all the files on the command line see the :mod:`fileinput`
module. For creating temporary files and directories see the :mod:`tempfile`
module, and for high-level file and directory handling see the :mod:`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 :mod:`os` module, but using them is of course a threat to
portability.
* An "Availability: Unix" note means that this function is commonly found on
Unix systems. It does not make any claims about its existence on a specific
operating system.
* If not separately noted, all functions that claim "Availability: Unix" are
supported on Mac OS X, which builds on a Unix core.
.. Availability notes get their own line and occur at the end of the function
.. documentation.
.. note::
All functions in this module raise :exc:`OSError` in the case of invalid or
inaccessible file names and paths, or other arguments that have the correct
type, but are not accepted by the operating system.
.. exception:: error
An alias for the built-in :exc:`OSError` exception.
.. data:: name
The name of the operating system dependent module imported. The following
names have currently been registered: ``'posix'``, ``'nt'``,
``'os2'``, ``'ce'``, ``'java'``, ``'riscos'``.
.. seealso::
:attr:`sys.platform` has a finer granularity. :func:`os.uname` gives
system-dependent version information.
The :mod:`platform` module provides detailed checks for the
system's identity.
.. _os-procinfo:
Process Parameters
------------------
These functions and data items provide information and operate on the current
process and user.
.. data:: environ
A :term:`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
:c:func:`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``, and when
one of the :meth:`pop` or :meth:`clear` methods is called.
.. versionchanged:: 2.6
Also unset environment variables when calling :meth:`os.environ.clear`
and :meth:`os.environ.pop`.
.. 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's 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.
.. note::
On Mac OS X, :func:`getgroups` behavior differs somewhat from
other Unix platforms. If the Python interpreter was built with a
deployment target of :const:`10.5` or earlier, :func:`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 :func:`setgroups` if suitably privileged.
If built with a deployment target greater than :const:`10.5`,
:func:`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 :func:`setgroups`, and its length is not limited to 16. The
deployment target value, :const:`MACOSX_DEPLOYMENT_TARGET`, can be
obtained with :func:`sysconfig.get_config_var`.
.. function:: initgroups(username, gid)
Call the system initgroups() to initialize the group access list with all of
the groups of which the specified username is a member, plus the specified
group id.
Availability: Unix.
.. versionadded:: 2.7
.. 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 process's real
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:: getresuid()
Return a tuple (ruid, euid, suid) denoting the current process's
real, effective, and saved user ids.
Availability: Unix.
.. versionadded:: 2.7
.. function:: getresgid()
Return a tuple (rgid, egid, sgid) denoting the current process's
real, effective, and saved group ids.
Availability: Unix.
.. versionadded:: 2.7
.. function:: getuid()
.. index:: single: user; id
Return the current process's real 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 typically available only to the superuser.
Availability: Unix.
.. versionadded:: 2.2
.. note:: On Mac OS X, the length of *groups* may not exceed the
system-defined maximum number of effective group ids, typically 16.
See the documentation for :func:`getgroups` for cases where it may not
return the same group list set by calling setgroups().
.. function:: setpgrp()
Call the system call :c:func:`setpgrp` or ``setpgrp(0, 0)`` depending on
which version is implemented (if any). See the Unix manual for the semantics.
Availability: Unix.
.. function:: setpgid(pid, pgrp)
Call the system call :c:func:`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:: setregid(rgid, egid)
Set the current process's real and effective group ids.
Availability: Unix.
.. function:: setresgid(rgid, egid, sgid)
Set the current process's real, effective, and saved group ids.
Availability: Unix.
.. versionadded:: 2.7
.. function:: setresuid(ruid, euid, suid)
Set the current process's real, effective, and saved user ids.
Availability: Unix.
.. versionadded:: 2.7
.. function:: setreuid(ruid, euid)
Set the current process's real and effective user ids.
Availability: Unix.
.. function:: getsid(pid)
Call the system call :c:func:`getsid`. See the Unix manual for the semantics.
Availability: Unix.
.. versionadded:: 2.4
.. function:: setsid()
Call the system call :c:func:`setsid`. See the Unix manual for the semantics.
Availability: Unix.
.. function:: setuid(uid)
.. index:: single: user; id, setting
Set the current process's 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*.
On platforms where :c:func:`strerror` returns ``NULL`` when given an unknown
error number, :exc:`ValueError` is raised.
Availability: Unix, Windows.
.. function:: umask(mask)
Set the current numeric umask and return 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`.
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``.
Availability: most flavors of Unix, Windows.
.. _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. If :func:`fdopen` raises an
exception, it leaves *fd* untouched (unclosed).
Availability: 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 :c:func:`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:`~file.close` method of the file object,
except that when the exit status is zero (termination without errors), ``None``
is returned.
Availability: Unix, Windows.
.. deprecated:: 2.6
This function is obsolete. Use the :mod:`subprocess` module. Check
especially the :ref:`subprocess-replacements` section.
.. versionchanged:: 2.0
This function worked unreliably under Windows in earlier versions of Python.
This was due to the use of the :c:func:`_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: Unix, Windows.
There are a number of different :func:`popen\*` functions that provide slightly
different ways to create subprocesses.
.. deprecated:: 2.6
All of the :func:`popen\*` functions are obsolete. Use the :mod:`subprocess`
module.
For each of the :func:`popen\*` variants, if *bufsize* is specified, it
specifies the buffer size for the I/O pipes. *mode*, if provided, should be the
string ``'b'`` or ``'t'``; on Windows this is needed to determine whether the
file objects should be opened in binary or text mode. The default value for
*mode* is ``'t'``.
Also, for each of these variants, on Unix, *cmd* may be a sequence, in which
case arguments will be passed directly to the program without shell intervention
(as with :func:`os.spawnv`). If *cmd* is a string it will be passed to the shell
(as with :func:`os.system`).
These methods do not make it possible to retrieve the exit status from the child
processes. The only way to control the input and output streams and also
retrieve the return codes is to use the :mod:`subprocess` module; these are only
available on Unix.
For a discussion of possible deadlock conditions related to the use of these
functions, see :ref:`popen2-flow-control`.
.. function:: popen2(cmd[, mode[, bufsize]])
Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
child_stdout)``.
.. deprecated:: 2.6
This function is obsolete. Use the :mod:`subprocess` module. Check
especially the :ref:`subprocess-replacements` section.
Availability: Unix, Windows.
.. versionadded:: 2.0
.. function:: popen3(cmd[, mode[, bufsize]])
Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
child_stdout, child_stderr)``.
.. deprecated:: 2.6
This function is obsolete. Use the :mod:`subprocess` module. Check
especially the :ref:`subprocess-replacements` section.
Availability: Unix, Windows.
.. versionadded:: 2.0
.. function:: popen4(cmd[, mode[, bufsize]])
Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
child_stdout_and_stderr)``.
.. deprecated:: 2.6
This function is obsolete. Use the :mod:`subprocess` module. Check
especially the :ref:`subprocess-replacements` section.
Availability: Unix, Windows.
.. versionadded:: 2.0
(Note that ``child_stdin, child_stdout, and child_stderr`` are named from the
point of view of the child process, so *child_stdin* is the child's standard
input.)
This functionality is also available in the :mod:`popen2` module using functions
of the same names, but the return values of those functions have a different
order.
.. _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.
The :meth:`~file.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.
.. function:: close(fd)
Close file descriptor *fd*.
Availability: Unix, Windows.
.. note::
This function is intended for low-level I/O and must be applied to a file
descriptor as returned by :func:`os.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:`~io.IOBase.close` method.
.. function:: closerange(fd_low, fd_high)
Close all file descriptors from *fd_low* (inclusive) to *fd_high* (exclusive),
ignoring errors. Equivalent to::
for fd in xrange(fd_low, fd_high):
try:
os.close(fd)
except OSError:
pass
Availability: Unix, Windows.
.. versionadded:: 2.6
.. function:: dup(fd)
Return a duplicate of file descriptor *fd*.
Availability: Unix, Windows.
.. function:: dup2(fd, fd2)
Duplicate file descriptor *fd* to *fd2*, closing the latter first if necessary.
Availability: Unix, Windows.
.. function:: fchmod(fd, mode)
Change the mode of the file given by *fd* to the numeric *mode*. See the docs
for :func:`chmod` for possible values of *mode*.
Availability: Unix.
.. versionadded:: 2.6
.. function:: 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.
Availability: Unix.
.. versionadded:: 2.6
.. function:: fdatasync(fd)
Force write of file with filedescriptor *fd* to disk. Does not force update of
metadata.
Availability: Unix.
.. note::
This function is not available on MacOS.
.. 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.
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.
Availability: Unix.
.. function:: fstat(fd)
Return status for file descriptor *fd*, like :func:`~os.stat`.
Availability: 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 :c:func:`fsync` function; on Windows, the MS :c:func:`_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: 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: Unix.
.. function:: isatty(fd)
Return ``True`` if the file descriptor *fd* is open and connected to a
tty(-like) device, else ``False``.
.. function:: lseek(fd, pos, how)
Set the current position of file descriptor *fd* to position *pos*, modified
by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
current position; :const:`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.
Availability: Unix, Windows.
.. data:: SEEK_SET
SEEK_CUR
SEEK_END
Parameters to the :func:`lseek` function. Their values are 0, 1, and 2,
respectively.
Availability: Windows, Unix.
.. versionadded:: 2.5
.. 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.
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 :ref:`open-constants`). In particular, on Windows adding
:const:`O_BINARY` is needed to open files in binary mode.
Availability: Unix, Windows.
.. 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:`~file.read` and :meth:`~file.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: some flavors of Unix.
.. function:: pipe()
Create a pipe. Return a pair of file descriptors ``(r, w)`` usable for reading
and writing, respectively.
Availability: 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: Unix, Windows.
.. note::
This function is intended for low-level I/O and must be applied to a file
descriptor as returned by :func:`os.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 :data:`sys.stdin`, use its :meth:`~file.read` or
:meth:`~file.readline` methods.
.. function:: tcgetpgrp(fd)
Return the process group associated with the terminal given by *fd* (an open
file descriptor as returned by :func:`os.open`).
Availability: Unix.
.. function:: tcsetpgrp(fd, pg)
Set the process group associated with the terminal given by *fd* (an open file
descriptor as returned by :func:`os.open`) to *pg*.
Availability: 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: Unix.
.. function:: write(fd, str)
Write the string *str* to file descriptor *fd*. Return the number of bytes
actually written.
Availability: Unix, Windows.
.. note::
This function is intended for low-level I/O and must be applied to a file
descriptor as returned by :func:`os.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 :data:`sys.stdout` or :data:`sys.stderr`, use its
:meth:`~file.write` method.
.. _open-constants:
``open()`` flag constants
~~~~~~~~~~~~~~~~~~~~~~~~~
The following constants are options for the *flags* parameter to the
:func:`~os.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 :manpage:`open(2)` manual page on Unix
or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windows.
.. data:: O_RDONLY
O_WRONLY
O_RDWR
O_APPEND
O_CREAT
O_EXCL
O_TRUNC
The above constants are available on Unix and Windows.
.. data:: O_DSYNC
O_RSYNC
O_SYNC
O_NDELAY
O_NONBLOCK
O_NOCTTY
The above constants are only available on Unix.
.. data:: O_BINARY
O_NOINHERIT
O_SHORT_LIVED
O_TEMPORARY
O_RANDOM
O_SEQUENTIAL
O_TEXT
The above constants are only available on Windows.
.. data:: O_ASYNC
O_DIRECT
O_DIRECTORY
O_NOFOLLOW
O_NOATIME
O_SHLOCK
O_EXLOCK
The above constants are extensions and not present if they are not
defined by the C library.
.. _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: 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. It's preferable to use :term:`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 IOError as e:
if e.errno == errno.EACCES:
return "some default data"
# Not a permission error.
raise
else:
with fp:
return fp.read()
.. 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: 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: Unix, Windows.
.. function:: getcwdu()
Return a Unicode object representing the current working directory.
Availability: 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):
* :data:`stat.UF_NODUMP`
* :data:`stat.UF_IMMUTABLE`
* :data:`stat.UF_APPEND`
* :data:`stat.UF_OPAQUE`
* :data:`stat.UF_NOUNLINK`
* :data:`stat.UF_COMPRESSED`
* :data:`stat.UF_HIDDEN`
* :data:`stat.SF_ARCHIVED`
* :data:`stat.SF_IMMUTABLE`
* :data:`stat.SF_APPEND`
* :data:`stat.SF_NOUNLINK`
* :data:`stat.SF_SNAPSHOT`
Availability: Unix.
.. versionadded:: 2.6
.. function:: chroot(path)
Change the root directory of the current process to *path*. Availability:
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 ORed
combinations of them:
* :data:`stat.S_ISUID`
* :data:`stat.S_ISGID`
* :data:`stat.S_ENFMT`
* :data:`stat.S_ISVTX`
* :data:`stat.S_IREAD`
* :data:`stat.S_IWRITE`
* :data:`stat.S_IEXEC`
* :data:`stat.S_IRWXU`
* :data:`stat.S_IRUSR`
* :data:`stat.S_IWUSR`
* :data:`stat.S_IXUSR`
* :data:`stat.S_IRWXG`
* :data:`stat.S_IRGRP`
* :data:`stat.S_IWGRP`
* :data:`stat.S_IXGRP`
* :data:`stat.S_IRWXO`
* :data:`stat.S_IROTH`
* :data:`stat.S_IWOTH`
* :data:`stat.S_IXOTH`
Availability: 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: 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:: 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 :func:`chmod`
for possible values of *mode*.
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: Unix.
.. versionadded:: 2.3
.. function:: link(source, link_name)
Create a hard link pointing to *source* named *link_name*.
Availability: Unix.
.. function:: listdir(path)
Return a list containing the names of the entries in the directory given by
*path*. The list is in arbitrary order. It does not include the special
entries ``'.'`` and ``'..'`` even if they are present in the
directory.
Availability: 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. Undecodable filenames will still be returned as
string objects.
.. function:: lstat(path)
Perform the equivalent of an :c:func:`lstat` system call on the given path.
Similar to :func:`~os.stat`, but does not follow symbolic links. On
platforms that do not support symbolic links, this is an alias for
:func:`~os.stat`.
.. 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: 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=0]])
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)
Extract the device major number from a raw device number (usually the
:attr:`st_dev` or :attr:`st_rdev` field from :c:type:`stat`).
.. versionadded:: 2.3
.. function:: minor(device)
Extract the device minor number from a raw device number (usually the
:attr:`st_dev` or :attr:`st_rdev` field from :c:type:`stat`).
.. versionadded:: 2.3
.. function:: makedev(major, minor)
Compose 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). If the directory already exists,
:exc:`OSError` is raised.
.. _mkdir_modebits:
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
:func:`chmod` explicitly to set them.
It is also possible to create temporary directories; see the
:mod:`tempfile` module's :func:`tempfile.mkdtemp` function.
Availability: 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. Raises an
:exc:`error` exception if the leaf directory already exists or cannot be
created. The default *mode* is ``0777`` (octal).
The *mode* parameter is passed to :func:`mkdir`; see :ref:`the mkdir()
description <mkdir_modebits>` for how it is interpreted.
.. note::
:func:`makedirs` will become confused if the path elements to create include
:data:`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.
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.
Availability: Unix.
.. 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:
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: Unix.
.. function:: remove(path)
Remove (delete) 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: Unix, Windows.
.. function:: removedirs(path)
.. index:: single: directory; deleting
Remove 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 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). 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: 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 (delete) the directory *path*. Only works when the directory is
empty, otherwise, :exc:`OSError` is raised. In order to remove whole
directory trees, :func:`shutil.rmtree` can be used.
Availability: Unix, Windows.
.. function:: stat(path)
Perform the equivalent of a :c:func:`stat` system call on the given path.
(This function follows symlinks; to stat a symlink use :func:`lstat`.)
The return value is an object whose attributes correspond to the members
of the :c:type:`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)
.. 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.
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 512-byte blocks allocated for file
* :attr:`st_blksize` - filesystem blocksize for efficient file system I/O
* :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 RISCOS systems, the following attributes are also available:
* :attr:`st_ftype` (file type)
* :attr:`st_attrs` (attributes)
* :attr:`st_obtype` (object type).
.. note::
The exact meaning and resolution of the :attr:`st_atime`,
:attr:`st_mtime`, and :attr:`st_ctime` attributes depend 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.
For backward compatibility, the return value of :func:`~os.stat` is also accessible
as a tuple of at least 10 integers giving the most important (and portable)
members of the :c:type:`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.
.. index:: module: stat
The standard module :mod:`stat` defines functions and constants that are useful
for extracting information from a :c:type:`stat` structure. (On Windows, some
items are filled with dummy values.)
Example::
>>> import os
>>> statinfo = os.stat('somefile.txt')
>>> statinfo
(33188, 422511, 769, 1, 1032, 100, 926, 1105022698,1105022732, 1105022732)
>>> statinfo.st_size
926
Availability: Unix, Windows.
.. versionchanged:: 2.2
Added access to values as attributes of the returned object.
.. versionchanged:: 2.5
Added :attr:`st_gen` and :attr:`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:`~os.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 :c:func:`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 :c:type:`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`.
.. 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 :c:type:`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.
Availability: Unix.
.. versionchanged:: 2.2
Added access to values as attributes of the returned object.
.. function:: symlink(source, link_name)
Create a symbolic link pointing to *source* named *link_name*.
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 :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: 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 (delete) the file *path*. This is the same function as
:func:`remove`; the :func:`unlink` name is its traditional Unix
name.
Availability: 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. (The effect is similar to running the Unix program :program:`touch` on
the path.) 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:`~os.stat` call, depending on the resolution with which your
operating system records access and modification times; see :func:`~os.stat`.
.. versionchanged:: 2.0
Added support for ``None`` for *times*.
Availability: Unix, Windows.
.. function:: walk(top, topdown=True, onerror=None, followlinks=False)
.. index::
single: directory; walking
single: directory; traversal
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 :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`` 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 :func:`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\* <execl>` 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 :c:func:`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 calling this function will not call the
Python signal handler registered for :const:`SIGABRT` with
:func:`signal.signal`.
Availability: 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 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
:func:`sys.stdout.flush` or :func:`os.fsync` before calling an
:func:`exec\* <execl>` function.
The "l" and "v" variants of the :func:`exec\* <execl>` 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 <execl>` 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 (these are used
instead of the current process' environment); the functions :func:`execl`,
:func:`execlp`, :func:`execv`, and :func:`execvp` all cause the new process to
inherit the environment of the current process.
Availability: Unix, Windows.
.. function:: _exit(n)
Exit the process with status *n*, without calling cleanup handlers, flushing
stdio buffers, etc.
Availability: 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 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: 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: Unix.
.. versionadded:: 2.3
.. data:: EX_DATAERR
Exit code that means the input data was incorrect.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_NOINPUT
Exit code that means an input file did not exist or was not readable.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_NOUSER
Exit code that means a specified user did not exist.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_NOHOST
Exit code that means a specified host did not exist.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_UNAVAILABLE
Exit code that means that a required service is unavailable.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_SOFTWARE
Exit code that means an internal software error was detected.
Availability: 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: 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: Unix.
.. versionadded:: 2.3
.. data:: EX_CANTCREAT
Exit code that means a user specified output file could not be created.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_IOERR
Exit code that means that an error occurred while doing I/O on some file.
Availability: 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: Unix.
.. versionadded:: 2.3
.. data:: EX_PROTOCOL
Exit code that means that a protocol exchange was illegal, invalid, or not
understood.
Availability: 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: Unix.
.. versionadded:: 2.3
.. data:: EX_CONFIG
Exit code that means that some kind of configuration error occurred.
Availability: Unix.
.. versionadded:: 2.3
.. data:: EX_NOTFOUND
Exit code that means something like "an entry was not found".
Availability: Unix.
.. versionadded:: 2.3
.. function:: fork()
Fork a child process. Return ``0`` in the child and the child's process id in the
parent. If an error occurs :exc:`OSError` is raised.
Note that some platforms including FreeBSD <= 6.3, Cygwin and OS/2 EMX have
known issues when using fork() from a thread.
.. warning::
See :mod:`ssl` for applications that use the SSL module with fork().
Availability: 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. If an error occurs :exc:`OSError` is raised.
Availability: 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.
Windows: The :data:`signal.CTRL_C_EVENT` and
:data:`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 :func:`kill` additionally takes
process handles to be killed.
.. versionadded:: 2.7 Windows support
.. function:: killpg(pgid, sig)
.. index::
single: process; killing
single: process; signalling
Send the signal *sig* to the process group *pgid*.
Availability: Unix.
.. versionadded:: 2.3
.. function:: nice(increment)
Add *increment* to the process's "niceness". Return the new niceness.
Availability: Unix.
.. function:: plock(op)
Lock program segments into memory. The value of *op* (defined in
``<sys/lock.h>``) determines which segments are locked.
Availability: Unix.
.. function:: popen(...)
popen2(...)
popen3(...)
popen4(...)
: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. Check especially the
:ref:`subprocess-replacements` section.)
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\* <spawnl>` 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 <spawnl>` 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 (they are
used instead of the current process' environment); the functions
:func:`spawnl`, :func:`spawnlp`, :func:`spawnv`, and :func:`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 :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. :func:`spawnle` and
:func:`spawnve` are not thread-safe on Windows; we advise you to use the
:mod:`subprocess` module instead.
.. versionadded:: 1.6
.. data:: P_NOWAIT
P_NOWAITO
Possible values for the *mode* parameter to the :func:`spawn\* <spawnl>` 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: Unix, Windows.
.. versionadded:: 1.6
.. data:: P_WAIT
Possible value for the *mode* parameter to the :func:`spawn\* <spawnl>` 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: Unix, Windows.
.. versionadded:: 1.6
.. data:: P_DETACH
P_OVERLAY
Possible values for the *mode* parameter to the :func:`spawn\* <spawnl>` 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 :c:func:`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 :c:func:`system`, and has the same limitations.
Changes to :data:`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 :c:func:`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.
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. See the
:ref:`subprocess-replacements` section in the :mod:`subprocess` documentation
for some helpful recipes.
Availability: Unix, Windows.
.. 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.
On Windows, only the first two items are filled, the others are zero.
Availability: 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: 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*).
An :exc:`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 :func:`spawn\* <spawnl>`
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:`~resource.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:`~resource.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: 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: 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)
Return ``True`` if a core dump was generated for the process, otherwise
return ``False``.
Availability: Unix.
.. versionadded:: 2.3
.. function:: WIFCONTINUED(status)
Return ``True`` if the process has been continued from a job control stop,
otherwise return ``False``.
Availability: Unix.
.. versionadded:: 2.3
.. function:: WIFSTOPPED(status)
Return ``True`` if the process has been stopped, otherwise return
``False``.
Availability: Unix.
.. function:: WIFSIGNALED(status)
Return ``True`` if the process exited due to a signal, otherwise return
``False``.
Availability: Unix.
.. function:: WIFEXITED(status)
Return ``True`` if the process exited using the :manpage:`exit(2)` system call,
otherwise return ``False``.
Availability: 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: Unix.
.. function:: WSTOPSIG(status)
Return the signal which caused the process to stop.
Availability: Unix.
.. function:: WTERMSIG(status)
Return the signal which caused the process to exit.
Availability: 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.
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.
Availability: Unix
.. 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: 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.
Availability: Unix.
.. 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: 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: 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 :mod:`os.path` module.
.. data:: curdir
The constant string used by the operating system to refer to the current
directory. This is ``'.'`` for Windows and POSIX. Also available via
:mod:`os.path`.
.. data:: pardir
The constant string used by the operating system to refer to the parent
directory. This is ``'..'`` for Windows and POSIX. Also available via
:mod:`os.path`.
.. data:: 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
: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\* <execl>` and
:func:`spawn\*p\* <spawnl>` 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
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, ``'nul'`` for Windows. 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.
For an easy-to-use interface to the random number generator
provided by your platform, please see :class:`random.SystemRandom`.
.. versionadded:: 2.4