如何枚举组合字符串作为for..in循环的搜索范围？

Question

I worked out a code that make sense to me but not python since I'm new to python.

Check my code here:

checksum_algos = ['md5','sha1']

for filename in ["%smanifest-%s.txt" % (prefix for prefix in ['', 'tag'],  a for a in checksum_algos)]:
  f = os.path.join(self.path, filename)
  if isfile(f):
     yield f

My intention is to search filename in a list like :

['manifest-md5.txt','tagmanifest-md5.txt','manifest-sha1.txt','tagmanifest-sha1.txt']

but I got syntax problem to implement it.

Thanks for any help.

Answer 1

You're overthinking it.

for filename in ("%smanifest-%s.txt" % (prefix, a)
    for prefix in ['', 'tag'] for a in checksum_algos):

Answer 2

Or you need itertools.product() :

>>> import itertools

>>> [i for i in itertools.product(('', 'tag'), ('sha', 'md5'))]
[('', 'sha'), ('', 'md5'), ('tag', 'sha'), ('tag', 'md5')]

Answer 3

Using new style string formatting and itertools :

from itertools import product
["{0}manifest-{1}.txt".format(i,e) for i,e in  product(*(tags,checksum_algos))]

out:

['manifest-md5.txt',
 'manifest-sha1.txt',
 'tagmanifest-md5.txt',
 'tagmanifest-sha1.txt']