Iterating over an unknown number of nested loops in python

问题

I have a variable number of user-defined lists, each containing words. For example, there may be three lists like the following:

list1 = ["THE", "A"]
list2 = ["ELEPHANT", "APPLE", "CAR"]
list3 = ["WALKED", "DROVE", "SAT"]

What I want is to iterate over every combination in each list, checking each against a dictionary of known words, to see which word-groupings are most like the dictionary. That means the iterations would be like:

[
    "THE ELEPHANT WALKED",
    "THE APPLE WALKED",
    "THE CAR WALKED",
    "THE ELEPHANT DROVE",
    "THE APPLE DROVE",
    "THE CAR DROVE",
    # ...
    "A CAR SAT",
]

The problem is that there can be any number of lists, and each list can contain a variable amount of items. I know that recursion could be used for this, but I need a solution without recursion. The problem I keep having is the fact that there can be a variable amount of lists, otherwise I would just write:

for a in list1:
    for b in list2:
        for c in list3:
            ...

But I won't know where to stop...

回答1:

itertools.product does exactly what you want:

from itertools import product

lists = [
    ['THE', 'A'],
    ['ELEPHANT', 'APPLE', 'CAR'],
    ['WALKED', 'DROVE', 'SAT']
]

for items in product(*lists):
    print items

回答2:

Using python 3.2

from itertools import product

[" ".join(i) for i in product(list1,list2,list3)]

来源：https://stackoverflow.com/questions/13443006/iterating-over-an-unknown-number-of-nested-loops-in-python