## 2012年5月9日 星期三

### [Python Std Library] File and Directory Access : os.path — Common pathname manipulations

Preface :
This module implements some useful functions on pathnames. To read or write files see open(), and for accessing the filesystem see the os module.
Note : On Windows, many of these functions do not properly support UNC pathnames. splitunc() and ismount() do handle them correctly.

Supported APIs :
os.path.abspath(path)
New in version 1.5.2.
Return a normalized absolutized version of the pathname path. On most platforms, this is equivalent to normpath(join(os.getcwd(), path)).
>>> os.getcwd()
'C:\\Users\\John' # 當前路徑
>>> os.path.abspath('./abc/test.txt')
'C:\\Users\\John\\abc\\test.txt' # 轉相對路徑為絕對路徑

os.path.basename(path)
Return the base name of pathname path. This is the second half of the pair returned by split(path).
>>> path = 'C:/Users/John/abc/'
>>> os.path.basename(path)
''
>>> path = 'C:/Users/John/abc/test.txt'
>>> os.path.basename(path)
'test.txt'

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.
>>> list = []
>>> list.append('/root/abc/123.txt')
>>> list.append('/root/abc/def/')
>>> list.append('/root/abc/test.txt')
>>> os.path.commonprefix(list)
'/root/abc/'

os.path.dirname(path)
Return the directory name of pathname path. This is the first half of the pair returned by split(path).
>>> path = "/root/abc/test.txt"
>>> os.path.dirname(path)
'/root/abc'

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.exists('C:/test.xml')
True # C:/test.xml 存在
>>> os.path.exists('C:/notexist')
False

os.path.lexists(path)
New in version 2.4.
Return True if path refers to an existing path. Returns True for broken symbolic links (does not follow symbolic links). Equivalent to exists() on platforms lackingos.lstat().

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)
New in version 1.5.2.
Changed in version 2.3: If os.stat_float_times() returns True, the result is a floating point number.

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 :

os.path.getmtime(path)
New in version 1.5.2.
Changed in version 2.3: If os.stat_float_times() returns True, the result is a floating point number.

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.

os.path.getctime(path)
New in version 2.3.
Return the system’s ctime which, on some systems (like Unix) is the time of the last 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.

os.path.getsize(path)
New in version 1.5.2.
Return the size, in bytes, of path. Raise os.error if the file does not exist or is inaccessible.

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. Usage as below :
>>> path = 'C:/abc/test.txt'
>>> os.path.isabs(path)
True
>>> os.path.isabs('./abc/test.txt')
False

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.

Return True if path refers to a directory entry that is a symbolic link. Always False if symbolic links are not supported.

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(path1[, path2[, ...]])
Join one or more path components intelligently. If any component is an absolute path, all previous components (on Windows, including the previous drive letter, if there was one) are thrown away, and joining continues. The return value is the concatenation of path1, and optionally path2, etc., with exactly one directory separator (os.sep) following each non-empty part except the last. (This means that an empty last part will result in a path that ends with a separator.) Note that on Windows, 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.join('C:\\', 'abc', '', 'def', 'test.txt')
'C:\\abc\\def\\test.txt'

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.normcase('/abc/def/test.txt')
'\\abc\\def\\test.txt'
>>> os.path.normcase('C:\\abc\\DEF/test.txt')
'c:\\abc\\def\\test.txt' # slash 被轉成 backward slash, 大寫轉小寫

os.path.normpath(path)
Normalize a pathname. This collapses redundant separators and up-level references so that A//BA/B/A/./B and A/foo/../B all become A/B.

It does not normalize the case (use normcase() for that). On Windows, it converts forward slashes to backward slashes. It should be understood that this may change the meaning of the path if it contains symbolic links!
>>> os.path.normpath('C:\\abc\\..\\DEF\\.\\test.txt')
'C:\\DEF\\test.txt' # 大小寫保留, .. 被轉換成前一層目錄, .\\ 被移除.

os.path.realpath(path)
New in version 2.2.
Return the canonical path of the specified filename, eliminating any symbolic links encountered in the path (if they are supported by the operating system).

os.path.relpath(path[, start])
New in version 2.6.
Availability: Windows, Unix.
Return a relative filepath to path either from the current directory or from an optional start point. start defaults to os.curdir.
>>> os.path.relpath('/root/test/abc/test.txt')
'../../root/test/abc/test.txt'
>>> os.getcwd() # 取回當前路徑
'/home/john'

os.path.samefile(path1, path2)
Availability: Unix.
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 a os.stat() call on either pathname fails.
>>> os.path.samefile('/home/john/Test/abc/test.txt', './sTest/test.txt')
True
>>> os.path.samefile('/home/john/Test/abc/test.txt', './sTest/test.txt1')
Traceback (most recent call last):
File "", line 1, in
File "/usr/lib/python2.6/posixpath.py", line 153, in samefile
s2 = os.stat(f2)
OSError: [Errno 2] No such file or directory: './sTest/test.txt1'

os.path.sameopenfile(fp1, fp2)
Availability: Unix.
Return True if the file descriptors fp1 and fp2 refer to the same file.

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 pathhead 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). Below are simple usages :
>>> os.path.split('/home/john/Test/abc/test.txt')
('/home/john/Test/abc', 'test.txt')
>>> os.path.split('/home/john/Test/abc/')
('/home/john/Test/abc', '')
>>> os.path.split('/home/john/Test/abc')
('/home/john/Test', 'abc')

os.path.splitdrive(path)
New in version 1.3.
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, drivewill always be the empty string. In all cases, drive + tail will be the same as path.
>>> os.path.splitdrive("C://abc/test.txt")
('C:', '//abc/test.txt')

os.path.splitext(path)
Changed in version 2.6: Earlier versions could produce an empty root when the only period was the first character.
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', '').
>>> os.path.splitext('/root/abc/test.txt')
('/root/abc/test', '.txt')
>>> os.path.splitext('/root/abc/test.123.txt')
('/root/abc/test.123', '.txt') # 只取最後一個 '.' 開始的副檔名
>>> os.path.splitext('/root/abc/test')
('/root/abc/test', '')

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 modifynames 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.)

os.path.supports_unicode_filenames
New in version 2.3.
True if arbitrary Unicode strings can be used as file names (within limitations imposed by the file system).
This message was edited 54 times. Last update was at 09/05/2012 16:16:20

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