cpython/Doc/library/os.path.rst

:mod:`os.path` --- Common pathname manipulations
================================================

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

.. 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 either strings,
or bytes. Applications are encouraged to represent file names as
(Unicode) character strings. Unfortunately, some file names may not be
representable as strings on Unix, so applications that need to support
arbitrary file names on Unix should use bytes objects to represent
path names. Vice versa, using bytes objects cannot represent all file
names on Windows (in the standard ``mbcs`` encoding), hence Windows
applications should use string objects to access all files.

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
   * :mod:`macpath` for old-style MacOS paths


.. function:: abspath(path)

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


.. 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 (``''``).


.. function:: commonpath(paths)

   Return the longest common sub-path of each pathname in the sequence
   *paths*.  Raise ValueError if *paths* contains both absolute and relative
   pathnames, or if *paths* is empty.  Unlike :func:`commonprefix`, this
   returns a valid path.

   Availability: Unix, Windows

   .. versionadded:: 3.5


.. function:: commonprefix(list)

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

   .. note::

      This function may return invalid paths because it works a
      character at a time.  To obtain a valid path, see
      :func:`commonpath`.

      ::

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

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


.. 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`.


.. 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.


.. function:: lexists(path)

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


.. 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:: 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:`HOME` and :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 stripping the last directory component
   from the created user path derived above.

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


.. 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}``.


.. function:: getatime(path)

   Return the time of last access of *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.

   If :func:`os.stat_float_times` returns ``True``, the result is a floating point
   number.


.. function:: getmtime(path)

   Return the time of last modification of *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.

   If :func:`os.stat_float_times` returns ``True``, the result is a floating point
   number.


.. 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.


.. function:: getsize(path)

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


.. 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 a (back)slash after chopping
   off a potential drive letter.


.. function:: isfile(path)

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


.. function:: isdir(path)

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


.. function:: islink(path)

   Return ``True`` if *path* refers to a directory entry that is a symbolic link.
   Always ``False`` if symbolic links are not supported by the python runtime.


.. 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.  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.

   .. versionadded:: 3.4
      Support for detecting non-root mount points on Windows.


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

   Join one or more path components intelligently.  The return value is the
   concatenation of *path* and any members of *\*paths* with exactly one
   directory separator (``os.sep``) following each non-empty part except the
   last, meaning that the result will only end in a separator if the last
   part is empty.  If a component is an absolute path, all previous
   components are thrown away and joining continues from the absolute path
   component.

   On Windows, the drive letter is not reset when an absolute path component
   (e.g., ``r'\foo'``) is encountered.  If a component contains a drive
   letter, all previous components are thrown away and the drive letter is
   reset.  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`.


.. function:: normcase(path)

   Normalize the case of a pathname.  On Unix and Mac OS X, this returns the
   path unchanged; on case-insensitive filesystems, it converts the path to
   lowercase.  On Windows, it also converts forward slashes to backward slashes.
   Raise a TypeError if the type of *path* is not ``str`` or ``bytes``.


.. 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`.


.. function:: realpath(path)

   Return the canonical path of the specified filename, eliminating any symbolic
   links encountered in the path (if they are supported by the operating system).


.. 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*.

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

   Availability: Unix, Windows.


.. 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 a :func:`os.stat` call on either pathname fails.

   Availability: Unix, Windows.

   .. versionchanged:: 3.2
      Added Windows support.

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


.. function:: sameopenfile(fp1, fp2)

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

   Availability: Unix, Windows.

   .. versionchanged:: 3.2
      Added Windows support.


.. 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`.

   Availability: Unix, Windows.

   .. 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:`dirname` and
   :func:`basename`.


.. 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.
   e.g. ``splitdrive("c:/dir")`` returns ``("c:", "/dir")``

   If the path contains a UNC path, drive will contain the host name
   and share, up to but not including the fourth separator.
   e.g. ``splitdrive("//host/computer/dir")`` returns ``("//host/computer", "/dir")``


.. function:: splitext(path)

   Split the pathname *path* into a pair ``(root, ext)``  such that ``root + ext ==
   path``, and *ext* is empty or begins with a period and contains at most one
   period. Leading periods on the basename are  ignored; ``splitext('.cshrc')``
   returns  ``('.cshrc', '')``.


.. function:: splitunc(path)

   .. deprecated:: 3.1
      Use *splitdrive* instead.

   Split the pathname *path* into a pair ``(unc, rest)`` so that *unc* is the UNC
   mount point (such as ``r'\\host\mount'``), if present, and *rest* the rest of
   the path (such as  ``r'\path\file.ext'``).  For paths containing drive letters,
   *unc* will always be the empty string.

   Availability:  Windows.


.. data:: supports_unicode_filenames

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