Python结构化循环多个项目

Question

I would like to loop over three lists

['A','B'],[1,2],[3,4]

If I wanted to loop over all possibilities, I could have done this:

for i,j,k in zip(['A','B'],[1,2],[3,4])

However, I want to loop in a certain manner. I want to iterate over 'A',1 and 'B',2 for all possible values of the last list. Thus I want to exclude the combinations

 'A',2 and 'B',1.

Basically I want to generate the following items. 'A',1,3 'A',1,4 'B',2,3 B',2,4

I am clueless on how to do it.

Answer 1

Because you want to keep 'a' tied together with 1, and 'b' with 2, you should zip the first two lists together. And because you want to iterate over 3 and 4 regardless of which choice you make in the first part, that should be a separate iteration, not part of the zip.

[(i,j,k) for k in [3, 4] for i,j in zip(['a', 'b'], [1, 2])]

# [('a', 1, 3), ('b', 2, 3), ('a', 1, 4), ('b', 2, 4)]

Answer 2

You could use itertools.product

from itertools import product
for a,b in product(zip(l1,l2), l3):
        print (a[0], a[1], b)

A 1 3
A 1 4
B 2 3
B 2 4