几个有用的python函数 (笛卡尔积, 排列, 组合)

product 笛卡尔积

permutations 排列

combinations 组合,没有重复

combinations_with_replacement 组合,有重复

详细的参见官网。

>>> import itertools
>>> for i in itertools.product('ABCD', repeat = 2):
...     print i,
... 
('A', 'A') ('A', 'B') ('A', 'C') ('A', 'D') ('B', 'A') ('B', 'B') ('B', 'C') ('B', 'D') ('C', 'A') ('C', 'B') ('C', 'C') ('C', 'D') ('D', 'A') ('D', 'B') ('D', 'C') ('D', 'D')
>>> for i in itertools.permutations('ABCD', 2):
...     print i,
... 
('A', 'B') ('A', 'C') ('A', 'D') ('B', 'A') ('B', 'C') ('B', 'D') ('C', 'A') ('C', 'B') ('C', 'D') ('D', 'A') ('D', 'B') ('D', 'C')
>>> for i in itertools.combinations('ABCD', 2):
...     print i,
... 
('A', 'B') ('A', 'C') ('A', 'D') ('B', 'C') ('B', 'D') ('C', 'D')
>>> for i in itertools.combinations_with_replacement('ABCD', 2):
...     print i,
... 
('A', 'A') ('A', 'B') ('A', 'C') ('A', 'D') ('B', 'B') ('B', 'C') ('B', 'D') ('C', 'C') ('C', 'D') ('D', 'D')

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