for file in os.listdir(path):
    if os.path.isfile(file) and os.path.splitext(file)[1] == '.txt':
      #打开txt文件，并提取数据

> os.listdir(path)
['cg.A.1.txt', 'cg.A.128.txt', 'cg.A.16.txt', 'cg.A.2.txt', 'cg.A.256.txt', 'cg.
A.32.txt', 'cg.A.4.txt', 'cg.A.512.txt', 'cg.A.64.txt', 'cg.A.8.txt', 'cg.B.1.tx
t', 'cg.B.128.txt', 'cg.B.16.txt', 'cg.B.2.txt', 'cg.B.256.txt', 'cg.B.32.txt',
'cg.B.4.txt', 'cg.B.512.txt', 'cg.B.64.txt', 'cg.B.8.txt', 'cg.C.1.txt', 'cg.C.1
28.txt', 'cg.C.16.txt', 'cg.C.2.txt', 'cg.C.256.txt', 'cg.C.32.txt', 'cg.C.4.txt
', 'cg.C.512.txt', 'cg.C.64.txt', 'cg.C.8.txt', 'cg.D.128.txt', 'cg.D.16.txt', '
cg.D.256.txt', 'cg.D.32.txt', 'cg.D.512.txt', 'cg.D.64.txt']
> files = os.listdir(path)
> os.path.isfile(files[1])
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.isfile(os.path.join(path,files[1]))
True