> import os
> for i in os.walk("."):
... print i[0],"\n##",i[1],"\n##",i[2]
... 
. #当前目录
## ['fa', 'out'] #当前目录中的子目录 
## ['meta_rna.sh', 'nohup.out', 'log.cpu', 'blast_seq.py']
./fa # 第一个子目录
## [] # 第一个子目录中的目录
## ['assemblyar_new_2.faa']
./out # 第二个子目录
## [] # 第二个子目录中的目录
## ['assemblyar_new_2.faa.coord', 'assemblyar_new_2.faa.mask', 'assemblyar_new_2.faa.seq', 'result_1.xm', 'result.xml', 'blast_seq.py']

> def VisitDir(arg, dirname, names):
... for filespath in names:
... print os.path.join(dirname, filespath)
... 
> path="."
> os.path.walk(path, VisitDir, ())
./meta_rna.sh
./fa
./out
./nohup.out
./log.cpu
./blast_seq.py
./fa/assemblyar_new_2.faa
./out/assemblyar_new_2.faa.coord
./out/assemblyar_new_2.faa.mask
./out/assemblyar_new_2.faa.seq
./out/result_1.xm
./out/result.xml
./out/blast_seq.py
> os.getcwd()
'/home/served_pro/Find_nick'
> abs_path= os.getcwd()
> os.path.walk(abs_path, VisitDir, ())
/home/served_pro/Find_nick/meta_rna.sh
/home/served_pro/Find_nick/fa
/home/served_pro/Find_nick/out
/home/served_pro/Find_nick/nohup.out
/home/served_pro/Find_nick/log.cpu
/home/served_pro/Find_nick/blast_seq.py
/home/served_pro/Find_nick/fa/assemblyar_new_2.faa
/home/served_pro/Find_nick/out/assemblyar_new_2.faa.coord
/home/served_pro/Find_nick/out/assemblyar_new_2.faa.mask
/home/served_pro/Find_nick/out/assemblyar_new_2.faa.seq
/home/served_pro/Find_nick/out/result_1.xm
/home/served_pro/Find_nick/out/result.xml
/home/served_pro/Find_nick/out/blast_seq.py

#方法1：使用os.listdir
import os
for filename in os.listdir(r'c:\\windows'):
print filename
#方法2：使用glob模块，可以设置文件过滤
import glob
for filename in glob.glob(r'c:\\windows\\*.exe'):
print filename
#方法3：通过os.path.walk递归遍历，可以访问子文件夹
import os.path
def processDirectory ( args, dirname, filenames ):
print 'Directory',dirname
for filename in filenames:
print ' File',filename
os.path.walk(r'c:\\windows', processDirectory, None )
#方法4：非递归
import os
for dirpath, dirnames, filenames in os.walk('c:\\\\winnt'):
print 'Directory', dirpath
for filename in filenames:
print ' File', filename

import os
os.path.isfile('test.txt') #如果不存在就返回False
os.path.exists(directory) #如果目录不存在就返回False