os.walk目录遍历<a id="sec-1" name="sec-1"></a>

每个月都有那么几天想划水，又到划水的日子了，今天分享的是刚在处理遍历目录相关用到的相关方法。

os.walk<a id="sec-1-1" name="sec-1-1"></a>

os.walk的参数如下:

os.walk(top, topdown=True, onerror=None, followlinks=False)

其中：

top是要遍历的目录。
topdown是代表要从上而下遍历还是从下往上遍历。
onerror可以用来设置当便利出现错误的处理函数(该函数接受一个OSError的实例作为参数)，设置为空则不作处理。
followlinks表示是否要跟随目录下的链接去继续遍历，要注意的是，os.walk不会记录已经遍历的目录，所以跟随链接遍历的话有可能一直循环调用下去。

os.walk返回的是一个3个元素的元组 (root, dirs, files) ，分别表示遍历的路径名，该路径下的目录列表和该路径下文件列表。注意目录列表和文件列表不是具体路径，需要具体路径(从root开始的路径)的话可以用 os.path.join(root,dir) 和 os.path.join(root,dir) 。

例子<a id="sec-1-2" name="sec-1-2"></a>

假设现在存在如下的文件和目录结构:

➜  test_os_walk git:(master) ✗ tree
.
├── a.py
├── b.py
├── c.py
├── dir1
│   ├── dir4
│   │   ├── g.py
│   │   └── h.py
│   ├── dirx
│   │   ├── diry
│   │   │   └── k.py
│   │   └── z.py
│   ├── e.py
│   ├── f.py
│   └── g.py
├── dir2
│   ├── dira
│   │   └── dirb
│   │       └── dirc
│   │           └── aha.py
│   ├── k.py
│   ├── l.py
│   └── m.py
└── dir3
    ├── dir5
    │   └── z.py
    ├── x.py
    └── y.py

10 directories, 17 files

测试topdown<a id="sec-1-2-1" name="sec-1-2-1"></a>

当我用 os.walk 遍历这个目录时，程序和输出如下:

import os

path = '/Users/nisen/Projects/python_advanced_class/test/test_os_walk'

for root, dirs, files in os.walk(path, True):
    print 'root: %s' % root
    print 'dirs: %s' % dirs
    print 'files: %s' % files
    print ''

结果如下，从root的路径可以看出遍历是自上而下的：

➜  test git:(master) ✗ python test11.py
root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk
dirs: ['dir1', 'dir2', 'dir3']
files: ['a.py', 'b.py', 'c.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1
dirs: ['dir4', 'dirx']
files: ['e.py', 'f.py', 'g.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dir4
dirs: []
files: ['g.py', 'h.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dirx
dirs: ['diry']
files: ['z.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dirx/diry
dirs: []
files: ['k.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2
dirs: ['dira']
files: ['k.py', 'l.py', 'm.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira
dirs: ['dirb']
files: []

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira/dirb
dirs: ['dirc']
files: []

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira/dirb/dirc
dirs: []
files: ['aha.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir3
dirs: ['dir5']
files: ['x.py', 'y.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir3/dir5
dirs: []
files: ['z.py']

而当设置os.walk的topdown为False时，结果如下, 可以看出他是自上而下遍历的：

➜  test git:(master) ✗ python test11.py
root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dir4
dirs: []
files: ['g.py', 'h.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dirx/diry
dirs: []
files: ['k.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1/dirx
dirs: ['diry']
files: ['z.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir1
dirs: ['dir4', 'dirx']
files: ['e.py', 'f.py', 'g.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira/dirb/dirc
dirs: []
files: ['aha.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira/dirb
dirs: ['dirc']
files: []

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2/dira
dirs: ['dirb']
files: []

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir2
dirs: ['dira']
files: ['k.py', 'l.py', 'm.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir3/dir5
dirs: []
files: ['z.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk/dir3
dirs: ['dir5']
files: ['x.py', 'y.py']

root: /Users/nisen/Projects/python_advanced_class/test/test_os_walk
dirs: ['dir1', 'dir2', 'dir3']
files: ['a.py', 'b.py', 'c.py']

运行时修改遍历目录<a id="sec-1-2-2" name="sec-1-2-2"></a>

当topdown设置为True时，可以在处理时修改返回的 dirs 列表，这样可以遍历下面的目录时会根据修改后的 dirs 来遍历。比如下面的例子，在遍历的时候不把"CSV"目录包括在内:

import os
from os.path import join, getsize
for root, dirs, files in os.walk('python/Lib/email'):
    print root, "consumes",
    print sum(getsize(join(root, name)) for name in files),
    print "bytes in", len(files), "non-directory files"
    if 'CVS' in dirs:
        dirs.remove('CVS')  # don't visit CVS directories

参考资料<a id="sec-2" name="sec-2"></a>

https://docs.python.org/2/library/os.html#os.walk

Python os.walk() 简介