如何使用itertools输出只有一定长度的结果

Question

假设我有一个字节列表(x00 to xFF)。如何使用itertools只返回有十 因此，例如，我想与长度为3的所有排列的长度排列，然后我会得到

[x00,x00,x00], [x00,x00,x01], ..., [xFF,xFF,xFF] 

这样，没有计算资源的浪费。

编辑：如果有更好的方法，不一定是itertools。

Answer 1

import itertools 
for tup in itertools.product(range(0x100), repeat=3): 
    ... 

Answer 2

itertools.combinations_with_replacement：

>>> my_list = [1, 2, 3, 4] 
>>> import itertools 
>>> 
>>> list(itertools.combinations_with_replacement(my_list, 3)) 
[(1, 1, 1), (1, 1, 2), (1, 1, 3), (1, 1, 4), 
(1, 2, 2), (1, 2, 3), (1, 2, 4), 
(1, 3, 3), (1, 3, 4), 
(1, 4, 4), 
(2, 2, 2), (2, 2, 3), (2, 2, 4), 
(2, 3, 3), (2, 3, 4), 
(2, 4, 4), 
(3, 3, 3), (3, 3, 4), 
(3, 4, 4), 
(4, 4, 4)] 

---

好像你希望所有的排列，与更换。在这种情况下，您需要：itertools.product正如在@ gnibbler的答案中一样。

Answer 3

看来@ gnibbler的解决方案更正确吗？

In [162]: >>> l = [1, 2, 3] 

In [163]: list(itertools.combinations_with_replacement(l, 3)) 
Out[163]: 
[(1, 1, 1), 
(1, 1, 2), 
(1, 1, 3), 
(1, 2, 2), 
(1, 2, 3), 
(1, 3, 3), 
(2, 2, 2), 
(2, 2, 3), 
(2, 3, 3), 
(3, 3, 3)] 

In [164]: list(itertools.product(l, repeat=3)) 
Out[164]: 
[(1, 1, 1), 
(1, 1, 2), 
(1, 1, 3), 
(1, 2, 1), 
(1, 2, 2), 
(1, 2, 3), 
(1, 3, 1), 
(1, 3, 2), 
(1, 3, 3), 
(2, 1, 1), 
(2, 1, 2), 
(2, 1, 3), 
(2, 2, 1), 
(2, 2, 2), 
(2, 2, 3), 
(2, 3, 1), 
(2, 3, 2), 
(2, 3, 3), 
(3, 1, 1), 
(3, 1, 2), 
(3, 1, 3), 
(3, 2, 1), 
(3, 2, 2), 
(3, 2, 3), 
(3, 3, 1), 
(3, 3, 2), 
(3, 3, 3)]