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

參考自 這裡
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.

- 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.

- 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//B, A/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 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). 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

[Python Std Library] Numeric and Math Modules : operator — Standard operators as functions

參考自 這裡 
Preface : 
The operator module exports a set of efficient functions corresponding to the intrinsic operators of Python. For example, operator.add(x, y) is equivalent to the expression x+y. The function names are those used for special class methods; variants without leading and trailing __ are also provided for convenience. 

Comparison operations : 
The functions fall into categories that perform object comparisons, logical operations, mathematical operations, sequence operations, and abstract type tests. The object comparison functions are useful for all objects, and are named after the rich comparison operators they support : 
operator.lt(a, b)/operator.__lt__(a, b) 
operator.le(a, b)/operator.__le__(a, b) 
operator.eq(a, b)/operator.__eq__(a, b) 
operator.ne(a, b)/operator.__ne__(a, b) 
operator.ge(a, b)/operator.__ge__(a, b) 
operator.gt(a, b)/operator.__gt__(a, b) 

New in version 2.2.
Perform "rich comparisons" between a and b. Specifically, lt(a, b) is equivalent to a < b, le(a, b) is equivalent to a <= b, eq(a, b) is equivalent to a == b, ne(a, b) is equivalent to a != b, gt(a, b) is equivalent to a > b and ge(a, b) is equivalent to a >= b. Note that unlike the built-in cmp(), these functions can return any value, which may or may not be interpretable as a Boolean value. See Comparisons for more information about rich comparisons.
底下為自訂義方法 __lt__() 的使用範例 :

Logical operations : 
The logical operations are also generally applicable to all objects, and support truth tests, identity tests, and boolean operations : 
- operator.not_(obj)/operator.__not__(obj) 

Return the outcome of not obj. (Note that there is no __not__() method for object instances; only the interpreter core defines this operation. The result is affected by the __nonzero__() and __len__() methods.)

更多 Logical operations 可以參考 這裡. 

The mathematical and bitwise operations : 
- operator.abs(obj)/operator.__abs__(obj) 

Return the absolute value of obj :

- operator.add(a, b)/operator.__add__(a, b) 

Return a + b, for a and b numbers :

- operator.and_(a, b)/operator.__and__(a, b) 

Return the bitwise and of a and b :

- operator.div(a, b)/operator.__div__(a, b) 

Return a / b when __future__.division is not in effect. This is also known as "classic" division :

- operator.floordiv(a, b)/operator.__floordiv__(a, b) 

New in version 2.2.
Return a // b.

- operator.index(a)/operator.__index__(a) 

New in version 2.5.
Return a converted to an integer. Equivalent to a.__index__().

- operator.invert(obj)/operator.__invert__(obj) 

Return the bitwise inverse of the number obj. This is equivalent to ~obj :

- operator.lshift(a, b)/operator.__lshift__(a, b) 

Return a shifted left by b :

- operator.mod(a, b)/operator.__mod__(a, b) 

Return a % b.

- operator.mul(a, b)/operator.__mul__(a, b) 

Return a * b, for a and b numbers.

- operator.neg(obj)/operator.__neg__(obj) 

Return obj negated (-obj).

- operator.or_(a, b)/operator.__or__(a, b) 

Return the bitwise or of a and b.

- operator.pos(obj)/operator.__pos__(obj) 

Return obj positive (+obj).

- operator.pow(a, b)/operator.__pow__(a, b) 

New in version 2.3.
Return a ** b, for a and b numbers.

- operator.rshift(a, b)/operator.__rshift__(a, b) 

Return a shifted right by b.

- operator.sub(a, b)/operator.__sub__(a, b) 

Return a - b :

- operator.truediv(a, b)/operator.__truediv__(a, b) 

New in version 2.2.
Return a / b when __future__.division is in effect. This is also known as “true” division :

Sequences operations : 
Operations which work with sequences (some of them with mappings too) include : 
- operator.concat(a, b)/operator.__concat__(a, b) 

Return a + b for a and b sequences :

- operator.contains(a, b)/operator.__contains__(a, b) 

New in version 2.0: The name __contains__().
Return the outcome of the test b in a. Note the reversed operands :

- operator.getitem(a, b)/operator.__getitem__(a, b) 

Return the value of a at index b :

- operator.setitem(a, b, c)/operator.__setitem__(a, b, c) 

Set the value of a at index b to c :

In-Place Operations : 
Many operations have an "in-place" version. The following functions provide a more primitive access to in-place operators than the usual syntax does; for example, thestatement x += y is equivalent to x = operator.iadd(x, y). Another way to put it like that z = operator.iadd(x, y) is equivalent to the compound statement z = x; z += y. 
- operator.iadd(a, b)/operator.__iadd__(a, b) 

New in version 2.5.
a = iadd(a, b) is equivalent to a += b :

更多 In-Place Operations 可以參考 這裡. 

Predicate Functions : 
The operator module also defines a few predicates to test the type of objects; however, these are not all reliable. It is preferable to test abstract base classes instead (see collections and numbers for details). 
- operator.isCallable(obj) 

Deprecated since version 2.0: Use isinstance(x, collections.Callable) instead.
Returns true if the object obj can be called like a function, otherwise it returns false. True is returned for functions, bound and unbound methods, class objects, and instance objects which support the __call__() method.

- operator.isMappingType(obj) 

Deprecated since version 2.7: Use isinstance(x, collections.Mapping) instead.
Returns true if the object obj supports the mapping interface. This is true for dictionaries and all instance objects defining __getitem__().

- operator.isNumberType(obj) 

Deprecated since version 2.7: Use isinstance(x, numbers.Number) instead.
Returns true if the object obj represents a number. This is true for all numeric types implemented in C.

- operator.isSequenceType(obj) 

Deprecated since version 2.7: Use isinstance(x, collections.Sequence) instead.
Returns true if the object obj supports the sequence protocol. This returns true for all objects which define sequence methods in C, and for all instance objects defining __getitem__().

Fields Extraction : 
The operator module also defines tools for generalized attribute and item lookups. These are useful for making fast field extractors as arguments for map(), sorted(),itertools.groupby(), or other functions that expect a function argument. 
- operator.attrgetter(attr[, args...]) 

New in version 2.4.
Changed in version 2.5: Added support for multiple attributes.
Changed in version 2.6: Added support for dotted attributes.
Return a callable object that fetches attr from its operand. If more than one attribute is requested, returns a tuple of attributes. After, f = attrgetter('name'), the callf(b) returns b.name. After, f = attrgetter('name', 'date'), the call f(b) returns (b.name, b.date). The attribute names can also contain dots; after f = attrgetter('date.month'), the call f(b) returns b.date.month :

- operator.itemgetter(item[, args...]) 

New in version 2.4.
Changed in version 2.5: Added support for multiple item extraction.
Return a callable object that fetches item from its operand using the operand’s __getitem__() method. If multiple items are specified, returns a tuple of lookup values. Return a callable object that fetches item from its operand using the operand’s __getitem__() method. If multiple items are specified, returns a tuple of lookup values. Usage example :


底下範例透過 operator.itemgetter() 與 map() 取出 sequence 中每個 tuple 的特定 element :

- operator.methodcaller(name[, args...]) 

New in version 2.6.
Return a callable object that calls the method name on its operand. If additional arguments and/or keyword arguments are given, they will be given to the method as well. After f = methodcaller('name'), the call f(b) returns b.name(). After f = methodcaller('name', 'foo', bar=1), the call f(b) returns b.name('foo', bar=1) :

Mapping Operators to Functions : 
This table shows how abstract operations correspond to operator symbols in the Python syntax and the functions in the operator module : 
 

Supplement : 
* [Python 學習筆記] 函式、類別與模組 : 類別 (特殊方法名稱) 
* Python 3.1 快速導覽 - 位元運算