itertools

0. Python中引入itertools

1. 笛卡尔积:

　product(iter1, iter2,...,iterN,[repeat=i])

 from itertools import product

 #笛卡尔积
 #3种常见的iter类型
 for x in product('',repeat=3):
     print(x)
 for x in product([1,0],repeat=3):
     print(x)
 for x in product((0,1),repeat=3):
     print(x)

结果

 ('', '', '')
 ('', '', '')
 ('', '', '')
 ('', '', '')
 ('', '', '')
 ('', '', '')
 ('', '', '')
 ('', '', '')

 (1, 1, 1)
 (1, 1, 0)
 (1, 0, 1)
 (1, 0, 0)
 (0, 1, 1)
 (0, 1, 0)
 (0, 0, 1)
 (0, 0, 0)

 (0, 0, 0)
 (0, 0, 1)
 (0, 1, 0)
 (0, 1, 1)
 (1, 0, 0)
 (1, 0, 1)
 (1, 1, 0)
 (1, 1, 1)

复杂示例

lucky+=[int(''.join([str(y) for y in x])) for x in list(product([4,7],repeat=i))]

2.全排列

　permutations(iterable,[,r])

 from itertools import permutations

 for x in permutations('ABC'):
     print(x)

结果

('A', 'B', 'C')
('A', 'C', 'B')
('B', 'A', 'C')
('B', 'C', 'A')
('C', 'A', 'B')
('C', 'B', 'A')

3. 组合

　combinations(iterable, r)

 from itertools import combinations

 for x in combinations('ABCD',):
     print(x)
 for x in combinations([,,,],):
     print(x)

结果

('A', 'B')
('A', 'C')
('B', 'C')
(, )
(, )
(, )

未完待续...