Python中的itertools.permutations

通俗地讲，就是返回可迭代对象的所有数学全排列方式。

Python 2.7.12 (default, Nov 20 2017, 18:23:56)
[GCC 5.4.0 20160609] on linux2
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>>> from itertools import permutations
>>> permutations(['a', 'b', 'c'])

>>> for item in permutations(['a', 'b', 'c']):
...     print item
...
('a', 'b', 'c')
('a', 'c', 'b')
('b', 'a', 'c')
('b', 'c', 'a')
('c', 'a', 'b')
('c', 'b', 'a')

>>> for i in itertools.permutations('123', 2):
...     print i
...
('1', '2')
('1', '3')
('2', '1')
('2', '3')
('3', '1')
('3', '2')
>>> itertools.permutations('123', 2)