10.1. "os.path" — Common pathname manipulations
***********************************************

This module implements some useful functions on pathnames. To read or
write files see "open()", and for accessing the filesystem see the
"os" module.

備註: On Windows, many of these functions do not properly support
  UNC pathnames. "splitunc()" and "ismount()" do handle them
  correctly.

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.)

備註: 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

  * "os2emxpath" for OS/2 EMX 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))".

   1.5.2 版新加入.

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
   ("''").

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 ("''"). Note that this may return invalid paths
   because it works a character at a time.

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()".

os.path.exists(path)

   Return "True" if *path* refers to an existing path.  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.

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()".

   2.4 版新加入.

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.

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}".

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 "os.error" if the file does not exist or is
   inaccessible.

   1.5.2 版新加入.

   2.3 版更變: 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 "os.error" if the file does not exist or is
   inaccessible.

   1.5.2 版新加入.

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

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 "os.error" if the file does not exist or is inaccessible.

   2.3 版新加入.

os.path.getsize(path)

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

   1.5.2 版新加入.

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.

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.

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.

os.path.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.

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.  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.

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".

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.

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()".

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).

   2.2 版新加入.

os.path.relpath(path[, start])

   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:  Windows, Unix.

   2.6 版新加入.

os.path.samefile(path1, path2)

   Return "True" if both pathname arguments refer to the same file or
   directory (as indicated by device number and i-node number). Raise
   an exception if an "os.stat()" call on either pathname fails.

   Availability: Unix.

os.path.sameopenfile(fp1, fp2)

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

   Availability: Unix.

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.

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()".

os.path.splitdrive(path)

   Split the pathname *path* into a pair "(drive, tail)" where *drive*
   is either a drive specification 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*.

   1.3 版新加入.

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', '')".

   2.6 版更變: Earlier versions could produce an empty root when the
   only period was the first character.

os.path.splitunc(path)

   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.walk(path, visit, arg)

   Calls the function *visit* with arguments "(arg, dirname, names)"
   for each directory in the directory tree rooted at *path*
   (including *path* itself, if it is a directory).  The argument
   *dirname* specifies the visited directory, the argument *names*
   lists the files in the directory (gotten from
   "os.listdir(dirname)"). The *visit* function may modify *names* to
   influence the set of directories visited below *dirname*, e.g. to
   avoid visiting certain parts of the tree.  (The object referred to
   by *names* must be modified in place, using "del" or slice
   assignment.)

   備註: Symbolic links to directories are not treated as
     subdirectories, and that "walk()" therefore will not visit them.
     To visit linked directories you must identify them with
     "os.path.islink(file)" and "os.path.isdir(file)", and invoke
     "walk()" as necessary.

   備註: This function is deprecated and has been removed in Python
     3 in favor of "os.walk()".

os.path.supports_unicode_filenames

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

   2.3 版新加入.
