11.2. "os.path" --- 常见路径操作
********************************

**Source code:** Lib/posixpath.py (for POSIX), Lib/ntpath.py (for
Windows NT), and Lib/macpath.py (for Macintosh)

======================================================================

This module implements some useful functions on pathnames. To read or
write files see "open()", and for accessing the filesystem see the
"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 "expanduser()" and "expandvars()" can be
invoked explicitly when an application desires shell-like path
expansion.  (See also the "glob" module.)

参见: The "pathlib" module offers high-level path objects.

注解: 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.

注解: Since different operating systems have different path name
  conventions, there are several versions of this module in the
  standard library.  The "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:

  * "posixpath" for UNIX-style paths

  * "ntpath" for Windows paths

  * "macpath" for old-style MacOS paths

os.path.abspath(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.basename(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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
   "commonprefix()", this returns a valid path.

   Availability: Unix, Windows

   3.5 新版功能.

   在 3.6 版更改: Accepts a sequence of *path-like objects*.

os.path.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 ("''").

   注解: This function may return invalid paths because it works a
     character at a time.  To obtain a valid path, see "commonpath()".

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

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.dirname(path)

   Return the directory name of pathname *path*.  This is the first
   element of the pair returned by passing *path* to the function
   "split()".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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 "os.stat()" on the requested file, even if the
   *path* physically exists.

   在 3.3 版更改: *path* can now be an integer: "True" is returned if
   it is an  open file descriptor, "False" otherwise.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.lexists(path)

   Return "True" if *path* refers to an existing path. Returns "True"
   for broken symbolic links.   Equivalent to "exists()" on platforms
   lacking "os.lstat()".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.expanduser(path)

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

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

   On Windows, "HOME" and "USERPROFILE" will be used if set, otherwise
   a combination of "HOMEPATH" and "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.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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}".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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
   "time" module).  Raise "OSError" if the file does not exist or is
   inaccessible.

   If "os.stat_float_times()" returns "True", the result is a floating
   point number.

os.path.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
   "time" module). Raise "OSError" if the file does not exist or is
   inaccessible.

   If "os.stat_float_times()" returns "True", the result is a floating
   point number.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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  "time" module).
   Raise "OSError" if the file does not exist or is inaccessible.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.getsize(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.isfile(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.isdir(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.islink(path)

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

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.ismount(path)

   Return "True" if pathname *path* is a *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, "path/..", is
   on a different device than *path*, or whether "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.

   3.4 新版功能: Support for detecting non-root mount points on
   Windows.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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 "C:" ("c:foo"), not
   "c:\foo".

   在 3.6 版更改: Accepts a *path-like object* for *path* and *paths*.

os.path.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" (directly or indirectly through
   the "os.PathLike" interface).

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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
   "normcase()".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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).

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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 "os.curdir".

   Availability: Unix, Windows.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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 "os.stat()" call on either
   pathname fails.

   Availability: Unix, Windows.

   在 3.2 版更改: Added Windows support.

   在 3.4 版更改: Windows now uses the same implementation as all
   other platforms.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.sameopenfile(fp1, fp2)

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

   Availability: Unix, Windows.

   在 3.2 版更改: Added Windows support.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.samestat(stat1, stat2)

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

   Availability: Unix, Windows.

   在 3.4 版更改: Added Windows support.

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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 "dirname()"
   and "basename()".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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")"

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.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', '')".

   在 3.6 版更改: 接受一个 *类路径对象*。

os.path.splitunc(path)

   3.1 版后已移除: 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.

os.path.supports_unicode_filenames

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