Python：创建N的组合，其中2个项目为常数

Question

Using itertools.combinations, the following works great:

for letter_group in itertools.combinations(alphabet, 5):
    print letter group

Now I want to have the first 2 of the 5 items in the combinations constant. Is there a way to do that?

For example, the output would then be:

(a,b,c,d,e)
(a,b,e,f,g)
...
(a,b,x,y,z)

Answer 1

Well, I think what you're trying to do is make 5-tuples where the first 2 are specified and the last 3 are from an iterable called alphabet , but where the last 3 can't reuse the first two.

How about this:

start = ('a', 'b')
for ending in itertools.combinations(set(alphabet) - set(start), 3):
    print start + ending

Answer 2

Just make your alphabet without the first two letters, do combinations of the rest, then contact ['a', 'b'] with the result, the runnable code:

# -*- coding: utf-8 -*-
import string
import itertools

alphabet = string.letters[:26]
prefix = ['a', 'b']

for letter_group in itertools.combinations(alphabet[len(prefix):], 3):
    print prefix + list(letter_group)