Python读取文件目录树——os.walk

os.walk是Python的内置函数用来遍历文件目录树。
import os

rootDir = 'd:\\assa'
for dirName, subdirList, fileList in os.walk(rootDir):
	print('Folder: %s' % dirName)
	for fname in fileList:
		print('\t%s' % fname)

目录结构为:

+test
	+f1
		2.txt
	+f2
		3.txt
	1.txt
输出结果为:
Folder: d:\Python Code\test
	1.txt
Folder: d:\Python Code\test\f1
	2.txt
Folder: d:\Python Code\test\f2
	3.txt
可以看到这是自顶向下的遍历顺序,如果我们要自底向上,先从最深处的文件开始遍历,可以加上topdown参数:
import os

rootDir = 'd:\\Python Code\\test'
for dirName, subdirList, fileList in os.walk(rootDir, topdown = False):
	print('Folder: %s' % dirName)
	for fname in fileList:
		print('\t%s' % fname)
结果:
Folder: d:\Python Code\test\f1
	2.txt
Folder: d:\Python Code\test\f2
	3.txt
Folder: d:\Python Code\test
	1.txt
如果想要在搜索的时候加上条件?比如跳过第一个文件夹,os.walk也可以做到:
import os

rootDir = 'd:\\Python Code\\test'
for dirName, subdirList, fileList in os.walk(rootDir):
	print('Folder: %s' % dirName)
	for fname in fileList:
		print('\t%s' % fname)
	if len(subdirList) > 0:
		del subdirList[0]
结果:
Folder: d:\Python Code\test
	1.txt
Folder: d:\Python Code\test\f2
	3.txt
有的同学却不能得到正确的结果,我们可以看看如下代码:
import os

rootDir = 'd:\\Python Code\\test'
for dirName, subdirList, fileList in os.walk(rootDir):
	print('Folder: %s' % dirName)
	for fname in fileList:
		print('\t%s' % fname)
	if len(subdirList) > 0:
		subdirList = subdirList[1:]

结果:

Folder: d:\Python Code\test
	1.txt
Folder: d:\Python Code\test\f1
	2.txt
Folder: d:\Python Code\test\f2
	3.txt

看起来和之前的版本相似,但是却不能得到期望的结果。这是因为我们没有就地改变subdirList的值:
>>> a=[1,2,3]
>>> id(a)
34006600
>>> del a[0]
>>> id(a)
34006600
>>> a = a[1:]
>>> id(a)
34006024

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