== os.path 模块 ==
``os.path`` 模块包含了各种处理长文件名(路径名)的函数. 先导入 (import) ``os``
模块, 然后就可以以 ``os.path`` 访问该模块.
=== 处理文件名===
``os.path`` 模块包含了许多与平台无关的处理长文件名的函数.
也就是说, 你不需要处理前后斜杠, 冒号等. 我们可以看看 [Example 1-42 #eg-1-42] 中的样例代码.
====Example 1-42. 使用 os.path 模块处理文件名====[eg-1-42]
```
File: os-path-example-1.py
import os
filename = "my/little/pony"
print "using", os.name, "..."
print "split", "=>", os.path.split(filename)
print "splitext", "=>", os.path.splitext(filename)
print "dirname", "=>", os.path.dirname(filename)
print "basename", "=>", os.path.basename(filename)
print "join", "=>", os.path.join(os.path.dirname(filename),
os.path.basename(filename))
*B*using nt ...
split => ('my/little', 'pony')
splitext => ('my/little/pony', '')
dirname => my/little
basename => pony
join => my/little\pony*b*
```
注意这里的 ``split`` 只分割出最后一项(不带斜杠).
``os.path`` 模块中还有许多函数允许你简单快速地获知文件名的一些特征，如 [Example 1-43 #eg-1-43] 所示。
====Example 1-43. 使用 os.path 模块检查文件名的特征====[eg-1-43]
```
File: os-path-example-2.py
import os
FILES = (
os.curdir,
"/",
"file",
"/file",
"samples",
"samples/sample.jpg",
"directory/file",
"../directory/file",
"/directory/file"
)
for file in FILES:
print file, "=>",
if os.path.exists(file):
print "EXISTS",
if os.path.isabs(file):
print "ISABS",
if os.path.isdir(file):
print "ISDIR",
if os.path.isfile(file):
print "ISFILE",
if os.path.islink(file):
print "ISLINK",
if os.path.ismount(file):
print "ISMOUNT",
print
*B*. => EXISTS ISDIR
/ => EXISTS ISABS ISDIR ISMOUNT
file =>
/file => ISABS
samples => EXISTS ISDIR
samples/sample.jpg => EXISTS ISFILE
directory/file =>
../directory/file =>
/directory/file => ISABS*b*
```
``expanduser`` 函数以与大部分Unix shell相同的方式处理用户名快捷符号(~,
不过在 Windows 下工作不正常), 如 [Example 1-44 #eg-1-44] 所示.
====Example 1-44. 使用 os.path 模块将用户名插入到文件名====[eg-1-44]
```
File: os-path-expanduser-example-1.py
import os
print os.path.expanduser("~/.pythonrc")
# /home/effbot/.pythonrc
```
``expandvars`` 函数将文件名中的环境变量替换为对应值, 如 [Example 1-45 #eg-1-45] 所示.
====Example 1-45. 使用 os.path 替换文件名中的环境变量====[eg-1-45]
```
File: os-path-expandvars-example-1.py
import os
os.environ["USER"] = "user"
print os.path.expandvars("/home/$USER/config")
print os.path.expandvars("$USER/folders")
*B*/home/user/config
user/folders*b*
```
=== 搜索文件系统===
``walk`` 函数会帮你找出一个目录树下的所有文件 (如 [Example 1-46 #eg-1-46]
所示). 它的参数依次是目录名, 回调函数, 以及传递给回调函数的数据对象.
====Example 1-46. 使用 os.path 搜索文件系统====[eg-1-46]
```
File: os-path-walk-example-1.py
import os
def callback(arg, directory, files):
for file in files:
print os.path.join(directory, file), repr(arg)
os.path.walk(".", callback, "secret message")
*B*./aifc-example-1.py 'secret message'
./anydbm-example-1.py 'secret message'
./array-example-1.py 'secret message'
...
./samples 'secret message'
./samples/sample.jpg 'secret message'
./samples/sample.txt 'secret message'
./samples/sample.zip 'secret message'
./samples/articles 'secret message'
./samples/articles/article-1.txt 'secret message'
./samples/articles/article-2.txt 'secret message'
...*b*
```
``walk`` 函数的接口多少有点晦涩 (也许只是对我个人而言, 我总是记不住参数的顺序).
[Example 1-47 #eg-1-47] 中展示的 ``index`` 函数会返回一个文件名列表,
你可以直接使用 ``for-in`` 循环处理文件.
====Example 1-47. 使用 os.listdir 搜索文件系统====[eg-1-47]
```
File: os-path-walk-example-2.py
import os
def index(directory):
# like os.listdir, but traverses directory trees
stack = [directory]
files = []
while stack:
directory = stack.pop()
for file in os.listdir(directory):
fullname = os.path.join(directory, file)
files.append(fullname)
if os.path.isdir(fullname) and not os.path.islink(fullname):
stack.append(fullname)
return files
for file in index("."):
print file
*B*.\aifc-example-1.py
.\anydbm-example-1.py
.\array-example-1.py
...*b*
```
如果你不想列出所有的文件 (基于性能或者是内存的考虑) , [Example 1-48 #eg-1-48] 展示了另一种方法.
这里 //DirectoryWalker// 类的行为与序列对象相似, 一次返回一个文件. (generator?)
====Example 1-48. 使用 DirectoryWalker 搜索文件系统====[eg-1-48]
```
File: os-path-walk-example-3.py
import os
class DirectoryWalker:
# a forward iterator that traverses a directory tree
def _ _init_ _(self, directory):
self.stack = [directory]
self.files = []
self.index = 0
def _ _getitem_ _(self, index):
while 1:
try:
file = self.files[self.index]
self.index = self.index + 1
except IndexError:
# pop next directory from stack
self.directory = self.stack.pop()
self.files = os.listdir(self.directory)
self.index = 0
else:
# got a filename
fullname = os.path.join(self.directory, file)
if os.path.isdir(fullname) and not os.path.islink(fullname):
self.stack.append(fullname)
return fullname
for file in DirectoryWalker("."):
print file
*B*.\aifc-example-1.py
.\anydbm-example-1.py
.\array-example-1.py
...*b*
```
注意 //DirectoryWalker// 类并不检查传递给 ``_ _getitem_ _`` 方法的索引值.
这意味着如果你越界访问序列成员(索引数字过大)的话, 这个类将不能正常工作.
最后, 如果你需要处理文件大小和时间戳, [Example 1-49 #eg-1-49] 给出了一个类,
它返回文件名和它的 ``os.stat`` 属性(一个元组). 这个版本在每个文件上都能节省一次或两次
``stat`` 调用( ``os.path.isdir`` 和 ``os.path.islink`` 内部都使用了 ``stat`` ),
并且在一些平台上运行很快.
====Example 1-49. 使用 DirectoryStatWalker 搜索文件系统====[eg-1-49]
```
File: os-path-walk-example-4.py
import os, stat
class DirectoryStatWalker:
# a forward iterator that traverses a directory tree, and
# returns the filename and additional file information
def _ _init_ _(self, directory):
self.stack = [directory]
self.files = []
self.index = 0
def _ _getitem_ _(self, index):
while 1:
try:
file = self.files[self.index]
self.index = self.index + 1
except IndexError:
# pop next directory from stack
self.directory = self.stack.pop()
self.files = os.listdir(self.directory)
self.index = 0
else:
# got a filename
fullname = os.path.join(self.directory, file)
st = os.stat(fullname)
mode = st[stat.ST_MODE]
if stat.S_ISDIR(mode) and not stat.S_ISLNK(mode):
self.stack.append(fullname)
return fullname, st
for file, st in DirectoryStatWalker("."):
print file, st[stat.ST_SIZE]
*B*.\aifc-example-1.py 336
.\anydbm-example-1.py 244
.\array-example-1.py 526*b*
```