如何让Python用固定的有限集中的元素打印给定长度的所有列表？

Question

For example, I would like to be able to get all lists of length 5 with elements in the set {0,1,2,3}.

I'm sure there is an easy answer but I am stuck and I don't see how to do it!

Answer 1

You're probably looking for itertools ' combinations_with_replacement :

list(itertools.combinations_with_replacement(range(4),2))
Out[18]: 
[(0, 0),
 (0, 1),
 (0, 2),
 (0, 3),
 (1, 1),
 (1, 2),
 (1, 3),
 (2, 2),
 (2, 3),
 (3, 3)]

(shown for n=2 for brevity)

Answer 2

If you don't count (1,2) and (2,1) as distinct, use roippi's answer. If you do, itertools.product (as in, "Cartesian product") works here:

>>> import itertools
>>> itertools.product(range(5), repeat=2)
[(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3), (3, 0), (3, 1), (3, 2), (3, 3)]

Answer 3

Do this:

import itertools    
list(itertools.product([0,1,2,3], repeat=5))

Combinations_with_replacement will catch all cases. It treats (a,b) as the same of (a,b). In practice, it will only output ordered results (ex. (1,3), but not (3,1))