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Doc/library/os.path.rst
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[3.13] gh-74453: Add stronger security warning to os.path.commonprefix
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:mod:`!os.path` --- Common pathname manipulations
=================================================

.. module:: os.path
   :synopsis: Operations on pathnames.

**Source code:** :source:`Lib/genericpath.py`, :source:`Lib/posixpath.py` (for POSIX) and
:source:`Lib/ntpath.py` (for Windows).

.. index:: single: path; operations

--------------

This module implements some useful functions on pathnames. To read or write
files see :func:`open`, and for accessing the filesystem see the :mod:`os`
module. The path parameters can be passed as strings, or bytes, or any object
implementing the :class:`os.PathLike` protocol.

Unlike a Unix shell, Python does not do any *automatic* path expansions.
Functions such as :func:`expanduser` and :func:`expandvars` can be invoked
explicitly when an application desires shell-like path expansion.  (See also
the :mod:`glob` module.)


.. seealso::
   The :mod:`pathlib` module offers high-level path objects.


.. note::

   All of these functions accept either only bytes or only string objects as
   their parameters.  The result is an object of the same type, if a path or
   file name is returned.

.. note::

   Since different operating systems have different path name conventions, there
   are several versions of this module in the standard library.  The
   :mod:`os.path` module is always the path module suitable for the operating
   system Python is running on, and therefore usable for local paths.  However,
   you can also import and use the individual modules if you want to manipulate
   a path that is *always* in one of the different formats.  They all have the
   same interface:

   * :mod:`!posixpath` for UNIX-style paths
   * :mod:`!ntpath` for Windows paths


.. versionchanged:: 3.8

   :func:`exists`, :func:`lexists`, :func:`isdir`, :func:`isfile`,
   :func:`islink`, and :func:`ismount` now return ``False`` instead of
   raising an exception for paths that contain characters or bytes
   unrepresentable at the OS level.


.. function:: abspath(path)

   Return a normalized absolutized version of the pathname *path*. On most
   platforms, this is equivalent to calling ``normpath(join(os.getcwd(), path))``.

   .. seealso:: :func:`os.path.join` and :func:`os.path.normpath`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: basename(path, /)

   Return the base name of pathname *path*.  This is the second element of the
   pair returned by passing *path* to the function :func:`split`.  Note that
   the result of this function is different
   from the Unix :program:`basename` program; where :program:`basename` for
   ``'/foo/bar/'`` returns ``'bar'``, the :func:`basename` function returns an
   empty string (``''``).

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: commonpath(paths)

   Return the longest common sub-path of each pathname in the iterable
   *paths*.  Raise :exc:`ValueError` if *paths* contain both absolute
   and relative pathnames, if *paths* are on different drives, or
   if *paths* is empty.  Unlike :func:`commonprefix`, this returns a
   valid path.

   .. versionadded:: 3.5

   .. versionchanged:: 3.6
      Accepts a sequence of :term:`path-like objects <path-like object>`.

   .. versionchanged:: 3.13
      Any iterable can now be passed, rather than just sequences.


.. function:: commonprefix(list, /)

   Return the longest string prefix (taken character-by-character) that is a
   prefix of all strings in *list*.  If *list* is empty, return the empty string
   (``''``).

   .. warning::

      This function may return invalid paths because it works a
      character at a time.
      If you need a **common path prefix**, then the algorithm
      implemented in this function is not secure. Use
      :func:`commonpath` for finding a common path prefix.

      ::

        >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
        '/usr/l'

        >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
        '/usr'

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: dirname(path, /)

   Return the directory name of pathname *path*.  This is the first element of
   the pair returned by passing *path* to the function :func:`split`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: exists(path)

   Return ``True`` if *path* refers to an existing path or an open
   file descriptor.  Returns ``False`` for broken symbolic links.  On
   some platforms, this function may return ``False`` if permission is
   not granted to execute :func:`os.stat` on the requested file, even
   if the *path* physically exists.

   .. versionchanged:: 3.3
      *path* can now be an integer: ``True`` is returned if it is an
       open file descriptor, ``False`` otherwise.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: lexists(path)

   Return ``True`` if *path* refers to an existing path, including
   broken symbolic links.   Equivalent to :func:`exists` on platforms lacking
   :func:`os.lstat`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. index:: single: ~ (tilde); home directory expansion

.. function:: expanduser(path)

   On Unix and Windows, return the argument with an initial component of ``~`` or
   ``~user`` replaced by that *user*'s home directory.

   .. index:: pair: module; pwd

   On Unix, an initial ``~`` is replaced by the environment variable :envvar:`HOME`
   if it is set; otherwise the current user's home directory is looked up in the
   password directory through the built-in module :mod:`pwd`. An initial ``~user``
   is looked up directly in the password directory.

   On Windows, :envvar:`USERPROFILE` will be used if set, otherwise a combination
   of :envvar:`HOMEPATH` and :envvar:`HOMEDRIVE` will be used.  An initial
   ``~user`` is handled by checking that the last directory component of the current
   user's home directory matches :envvar:`USERNAME`, and replacing it if so.

   If the expansion fails or if the path does not begin with a tilde, the path is
   returned unchanged.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.

   .. versionchanged:: 3.8
      No longer uses :envvar:`HOME` on Windows.

.. index::
   single: $ (dollar); environment variables expansion
   single: % (percent); environment variables expansion (Windows)

.. function:: expandvars(path)

   Return the argument with environment variables expanded.  Substrings of the form
   ``$name`` or ``${name}`` are replaced by the value of environment variable
   *name*.  Malformed variable names and references to non-existing variables are
   left unchanged.

   On Windows, ``%name%`` expansions are supported in addition to ``$name`` and
   ``${name}``.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: getatime(path, /)

   Return the time of last access of *path*.  The return value is a floating-point number giving
   the number of seconds since the epoch (see the  :mod:`time` module).  Raise
   :exc:`OSError` if the file does not exist or is inaccessible.


.. function:: getmtime(path, /)

   Return the time of last modification of *path*.  The return value is a floating-point number
   giving the number of seconds since the epoch (see the  :mod:`time` module).
   Raise :exc:`OSError` if the file does not exist or is inaccessible.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: getctime(path, /)

   Return the system's ctime which, on some systems (like Unix) is the time of the
   last metadata change, and, on others (like Windows), is the creation time for *path*.
   The return value is a number giving the number of seconds since the epoch (see
   the  :mod:`time` module).  Raise :exc:`OSError` if the file does not exist or
   is inaccessible.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: getsize(path, /)

   Return the size, in bytes, of *path*.  Raise :exc:`OSError` if the file does
   not exist or is inaccessible.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: isabs(path, /)

   Return ``True`` if *path* is an absolute pathname.  On Unix, that means it
   begins with a slash, on Windows that it begins with two (back)slashes, or a
   drive letter, colon, and (back)slash together.

   .. seealso:: :func:`abspath`

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.

   .. versionchanged:: 3.13
      On Windows, returns ``False`` if the given path starts with exactly one
      (back)slash.


.. function:: isfile(path)

   Return ``True`` if *path* is an :func:`existing <exists>` regular file.
   This follows symbolic links, so both :func:`islink` and :func:`isfile` can
   be true for the same path.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: isdir(path, /)

   Return ``True`` if *path* is an :func:`existing <exists>` directory.  This
   follows symbolic links, so both :func:`islink` and :func:`isdir` can be true
   for the same path.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: isjunction(path)

   Return ``True`` if *path* refers to an :func:`existing <lexists>` directory
   entry that is a junction.  Always return ``False`` if junctions are not
   supported on the current platform.

   .. versionadded:: 3.12


.. function:: islink(path)

   Return ``True`` if *path* refers to an :func:`existing <exists>` directory
   entry that is a symbolic link.  Always ``False`` if symbolic links are not
   supported by the Python runtime.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: ismount(path)

   Return ``True`` if pathname *path* is a :dfn:`mount point`: a point in a
   file system where a different file system has been mounted.  On POSIX, the
   function checks whether *path*'s parent, :file:`{path}/..`, is on a different
   device than *path*, or whether :file:`{path}/..` and *path* point to the same
   i-node on the same device --- this should detect mount points for all Unix
   and POSIX variants.  It is not able to reliably detect bind mounts on the
   same filesystem. On Linux systems, it will always return ``True`` for btrfs
   subvolumes, even if they aren't mount points. On Windows, a drive letter root
   and a share UNC are always mount points, and for any other path
   ``GetVolumePathName`` is called to see if it is different from the input path.

   .. versionchanged:: 3.4
      Added support for detecting non-root mount points on Windows.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: isdevdrive(path)

   Return ``True`` if pathname *path* is located on a Windows Dev Drive.
   A Dev Drive is optimized for developer scenarios, and offers faster
   performance for reading and writing files. It is recommended for use for
   source code, temporary build directories, package caches, and other
   IO-intensive operations.

   May raise an error for an invalid path, for example, one without a
   recognizable drive, but returns ``False`` on platforms that do not support
   Dev Drives. See `the Windows documentation <https://learn.microsoft.com/windows/dev-drive/>`_
   for information on enabling and creating Dev Drives.

   .. versionadded:: 3.12

   .. versionchanged:: 3.13
      The function is now available on all platforms, and will always return ``False`` on those that have no support for Dev Drives


.. function:: isreserved(path)

   Return ``True`` if *path* is a reserved pathname on the current system.

   On Windows, reserved filenames include those that end with a space or dot;
   those that contain colons (i.e. file streams such as "name:stream"),
   wildcard characters (i.e. ``'*?"<>'``), pipe, or ASCII control characters;
   as well as DOS device names such as "NUL", "CON", "CONIN$", "CONOUT$",
   "AUX", "PRN", "COM1", and "LPT1".

   .. note::

      This function approximates rules for reserved paths on most Windows
      systems. These rules change over time in various Windows releases.
      This function may be updated in future Python releases as changes to
      the rules become broadly available.

   .. availability:: Windows.

   .. versionadded:: 3.13


.. function:: join(path, /, *paths)

   Join one or more path segments intelligently.  The return value is the
   concatenation of *path* and all members of *\*paths*, with exactly one
   directory separator following each non-empty part, except the last. That is,
   the result will only end in a separator if the last part is either empty or
   ends in a separator.

   If a segment is an absolute path (which on Windows requires both a drive and
   a root), then all previous segments are ignored and joining continues from the
   absolute path segment. On Linux, for example::

      >>> os.path.join('/home/foo', 'bar')
      '/home/foo/bar'
      >>> os.path.join('/home/foo', '/home/bar')
      '/home/bar'

   On Windows, the drive is not reset when a rooted path segment (e.g.,
   ``r'\foo'``) is encountered. If a segment is on a different drive or is an
   absolute path, all previous segments are ignored and the drive is reset. For
   example::

      >>> os.path.join('c:\\', 'foo')
      'c:\\foo'
      >>> os.path.join('c:\\foo', 'd:\\bar')
      'd:\\bar'

   Note that since there is a current directory for each drive,
   ``os.path.join("c:", "foo")`` represents a path relative to the current
   directory on drive :file:`C:` (:file:`c:foo`), not :file:`c:\\foo`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object` for *path* and *paths*.


.. function:: normcase(path, /)

   Normalize the case of a pathname.  On Windows, convert all characters in the
   pathname to lowercase, and also convert forward slashes to backward slashes.
   On other operating systems, return the path unchanged.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: normpath(path)

   Normalize a pathname by collapsing redundant separators and up-level
   references so that ``A//B``, ``A/B/``, ``A/./B`` and ``A/foo/../B`` all
   become ``A/B``.  This string manipulation may change the meaning of a path
   that contains symbolic links.  On Windows, it converts forward slashes to
   backward slashes. To normalize case, use :func:`normcase`.

   .. note::
      On POSIX systems, in accordance with `IEEE Std 1003.1 2013 Edition; 4.13
      Pathname Resolution <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>`_,
      if a pathname begins with exactly two slashes, the first component
      following the leading characters may be interpreted in an implementation-defined
      manner, although more than two leading characters shall be treated as a
      single character.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: realpath(path, /, *, strict=False)

   Return the canonical path of the specified filename, eliminating any symbolic
   links encountered in the path (if they are supported by the operating
   system). On Windows, this function will also resolve MS-DOS (also called 8.3)
   style names such as ``C:\\PROGRA~1`` to ``C:\\Program Files``.

   By default, the path is evaluated up to the first component that does not
   exist, is a symlink loop, or whose evaluation raises :exc:`OSError`.
   All such components are appended unchanged to the existing part of the path.

   Some errors that are handled this way include "access denied", "not a
   directory", or "bad argument to internal function". Thus, the
   resulting path may be missing or inaccessible, may still contain
   links or loops, and may traverse non-directories.

   This behavior can be modified by keyword arguments:

   If *strict* is ``True``, the first error encountered when evaluating the path is
   re-raised.
   In particular, :exc:`FileNotFoundError` is raised if *path* does not exist,
   or another :exc:`OSError` if it is otherwise inaccessible.

   If *strict* is :py:data:`os.path.ALLOW_MISSING`, errors other than
   :exc:`FileNotFoundError` are re-raised (as with ``strict=True``).
   Thus, the returned path will not contain any symbolic links, but the named
   file and some of its parent directories may be missing.

   .. note::
      This function emulates the operating system's procedure for making a path
      canonical, which differs slightly between Windows and UNIX with respect
      to how links and subsequent path components interact.

      Operating system APIs make paths canonical as needed, so it's not
      normally necessary to call this function.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.

   .. versionchanged:: 3.8
      Symbolic links and junctions are now resolved on Windows.

   .. versionchanged:: 3.10
      The *strict* parameter was added.

   .. versionchanged:: 3.13.4
      The :py:data:`~os.path.ALLOW_MISSING` value for the *strict* parameter
      was added.

.. data:: ALLOW_MISSING

   Special value used for the *strict* argument in :func:`realpath`.

   .. versionadded:: 3.13.4

.. function:: relpath(path, start=os.curdir)

   Return a relative filepath to *path* either from the current directory or
   from an optional *start* directory.  This is a path computation:  the
   filesystem is not accessed to confirm the existence or nature of *path* or
   *start*.  On Windows, :exc:`ValueError` is raised when *path* and *start*
   are on different drives.

   *start* defaults to :data:`os.curdir`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: samefile(path1, path2, /)

   Return ``True`` if both pathname arguments refer to the same file or directory.
   This is determined by the device number and i-node number and raises an
   exception if an :func:`os.stat` call on either pathname fails.

   .. versionchanged:: 3.2
      Added Windows support.

   .. versionchanged:: 3.4
      Windows now uses the same implementation as all other platforms.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: sameopenfile(fp1, fp2)

   Return ``True`` if the file descriptors *fp1* and *fp2* refer to the same file.

   .. versionchanged:: 3.2
      Added Windows support.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: samestat(stat1, stat2, /)

   Return ``True`` if the stat tuples *stat1* and *stat2* refer to the same file.
   These structures may have been returned by :func:`os.fstat`,
   :func:`os.lstat`, or :func:`os.stat`.  This function implements the
   underlying comparison used by :func:`samefile` and :func:`sameopenfile`.

   .. versionchanged:: 3.4
      Added Windows support.


.. function:: split(path, /)

   Split the pathname *path* into a pair, ``(head, tail)`` where *tail* is the
   last pathname component and *head* is everything leading up to that.  The
   *tail* part will never contain a slash; if *path* ends in a slash, *tail*
   will be empty.  If there is no slash in *path*, *head* will be empty.  If
   *path* is empty, both *head* and *tail* are empty.  Trailing slashes are
   stripped from *head* unless it is the root (one or more slashes only).  In
   all cases, ``join(head, tail)`` returns a path to the same location as *path*
   (but the strings may differ).  Also see the functions :func:`join`,
   :func:`dirname` and :func:`basename`.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: splitdrive(path, /)

   Split the pathname *path* into a pair ``(drive, tail)`` where *drive* is either
   a mount point or the empty string.  On systems which do not use drive
   specifications, *drive* will always be the empty string.  In all cases, ``drive
   + tail`` will be the same as *path*.

   On Windows, splits a pathname into drive/UNC sharepoint and relative path.

   If the path contains a drive letter, drive will contain everything
   up to and including the colon::

      >>> splitdrive("c:/dir")
      ("c:", "/dir")

   If the path contains a UNC path, drive will contain the host name
   and share::

      >>> splitdrive("//host/computer/dir")
      ("//host/computer", "/dir")

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. function:: splitroot(path, /)

   Split the pathname *path* into a 3-item tuple ``(drive, root, tail)`` where
   *drive* is a device name or mount point, *root* is a string of separators
   after the drive, and *tail* is everything after the root. Any of these
   items may be the empty string. In all cases, ``drive + root + tail`` will
   be the same as *path*.

   On POSIX systems, *drive* is always empty. The *root* may be empty (if *path* is
   relative), a single forward slash (if *path* is absolute), or two forward slashes
   (implementation-defined per `IEEE Std 1003.1-2017; 4.13 Pathname Resolution
   <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>`_.)
   For example::

      >>> splitroot('/home/sam')
      ('', '/', 'home/sam')
      >>> splitroot('//home/sam')
      ('', '//', 'home/sam')
      >>> splitroot('///home/sam')
      ('', '/', '//home/sam')

   On Windows, *drive* may be empty, a drive-letter name, a UNC share, or a device
   name. The *root* may be empty, a forward slash, or a backward slash. For
   example::

      >>> splitroot('C:/Users/Sam')
      ('C:', '/', 'Users/Sam')
      >>> splitroot('//Server/Share/Users/Sam')
      ('//Server/Share', '/', 'Users/Sam')

   .. versionadded:: 3.12


.. function:: splitext(path, /)

   Split the pathname *path* into a pair ``(root, ext)``  such that ``root + ext ==
   path``, and the extension, *ext*, is empty or begins with a period and contains at
   most one period.

   If the path contains no extension, *ext* will be ``''``::

      >>> splitext('bar')
      ('bar', '')

   If the path contains an extension, then *ext* will be set to this extension,
   including the leading period. Note that previous periods will be ignored::

      >>> splitext('foo.bar.exe')
      ('foo.bar', '.exe')
      >>> splitext('/foo/bar.exe')
      ('/foo/bar', '.exe')

   Leading periods of the last component of the path are considered to
   be part of the root::

      >>> splitext('.cshrc')
      ('.cshrc', '')
      >>> splitext('/foo/....jpg')
      ('/foo/....jpg', '')

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.


.. data:: supports_unicode_filenames

   ``True`` if arbitrary Unicode strings can be used as file names (within limitations
   imposed by the file system).