用途
itertools.permutations：
>>> import itertools>>> stuff = [1, 2, 3]>>> for L in range(0, len(stuff)+1): for subset in itertools.permutations(stuff, L): print(subset)... ()(1,)(2,)(3,)(1, 2)(1, 3)(2, 1)(2, 3)(3, 1)....
帮助
itertools.permutations：
permutations(iterable[, r]) --> permutations objectReturn successive r-length permutations of elements in the iterable.permutations(range(3), 2) --> (0,1), (0,2), (1,0), (1,2), (2,0), (2,1)>>>
