Combinations of multiple lists

Question

Suppose I have three lists:

list1 --> [a, b, c, d, e, f, g, h]
list2 --> [i, j, k]
list3 --> [l, m, n, o, p]

I wish to generate all combinations where I take five elements from list1, two elements from list2 and three elements from list3.

eg.

a, b, c, d, e, i, j, l, m, n  
a, b, c, d, e, i, j, l, m, o
etc.

I tried to use itertools.combinations.

l1_combinations = itertools.combinations(list1, 5)
l2_combinations = itertools.combinations(list2, 2)
l3_combinations = itertools.combinations(list3, 3)
for l1_iterator in list(l1_combinations):
    for l2_iterator in list(l2_combinations): #added a missing )
        for l3_iterator in list(l3_combinations):
            sample = l1_iterator + l2_iterator + l3_iterator
            print(sample)

But I am getting output with iterations happening only on list3. In all the output, only first five elements from list1 and first two elements from list2 are present. Combinations with other elements from those two lists aren't present.

Can someone help me here and also explain what exactly did i miss ?

Answer 1

作为重新生成组合列表的替代方法，请预先计算组合的乘积；这也使您免于嵌套for循环。

from itertools import combinations, product


list1 = list("abcdefgh")
list2 = list("ijk")
list3 = list("lmnop")

l1 = combinations(list1, 5)
l2 = combinations(list2, 2)
l3 = combinations(list3, 3)
for c1, c2, c3 in product(l1, l2, l3):
    sample = c1 + c2 + c3
    print(sample)

Answer 2

第一次用尽后，请勿多次迭代同一个迭代器。每次迭代一个新的迭代器：

for l1_iterator in itertools.combinations(list1, 5):
    for l2_iterator in itertools.combinations(list2, 2):
        for l3_iterator in itertools.combinations(list3, 3):
            sample = l1_iterator + l2_iterator + l3_iterator
            print(sample)

或预先列出每个清单，以避免重新计算：

l1_combinations = list(itertools.combinations(list1, 5))
l2_combinations = list(itertools.combinations(list2, 2))
l3_combinations = list(itertools.combinations(list3, 3))
for l1_iterator in l1_combinations:
    for l2_iterator in l2_combinations:
        for l3_iterator in l3_combinations:
            sample = l1_iterator + l2_iterator + l3_iterator
            print(sample)