[英]How to use itertools to output results of only a certain length
假设我有一个字节列表(x00 to xFF)
。 如何使用itertools仅返回长度为X的排列。例如,我希望所有长度为3的排列,那么我将得到
[x00,x00,x00], [x00,x00,x01], ..., [xFF,xFF,xFF]
这样就不会浪费计算资源。
编辑:如果有更好的方法,不必一定是itertools。
import itertools
for tup in itertools.product(range(0x100), repeat=3):
...
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)]
似乎您希望所有置换都可以替换。 在这种情况下,您需要: itertools.product
如@gnibbler的答案。
看来@gnibbler的解决方案更正确?
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)]
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