问题：想要一个list中元素的两两组合、多个list元素的各种组合
解决：利用itertools.product(*iterables, repeat=2)求笛卡尔积即可
说明：笛卡尔积是两个集合x、y的笛卡尔积，表示为：x× y，结果是：第一个对象是x的成员，第二个对象是集合y中的任一元素，eg：x=(x1，x2)，y=(y1，y2)，则x × y=[(x1，y1)，(x1，y2)，(x2，y1)，(x2，y2)]

示例如下：

>>> from itertools import product
>>> list1 = ["x","y","z"]
>>> list2 = ["a","b","c"]
>>> list3 = [1,2,3]
>>> result = product(list1, repeat=2)
>>> list(result)
[('x', 'x'), ('x', 'y'), ('x', 'z'), ('y', 'x'), ('y', 'y'), ('y', 'z'), ('z', 'x'), ('z', 'y'), ('z', 'z')
>>> result = product(list1, list1)
>>> list(result)
[('x', 'x'), ('x', 'y'), ('x', 'z'), ('y', 'x'), ('y', 'y'), ('y', 'z'), ('z', 'x'), ('z', 'y'), ('z', 'z')]
>>> result = product(list1, list2)
>>> list(result)
[('x', 'a'), ('x', 'b'), ('x', 'c'), ('y', 'a'), ('y', 'b'), ('y', 'c'), ('z', 'a'), ('z', 'b'), ('z', 'c')]
>>> result = product(list1, list2, list3)
>>> for x in result:
...     print x
... 
('x', 'a', 1)
('x', 'a', 2)
('x', 'a', 3)
('x', 'b', 1)
('x', 'b', 2)
('x', 'b', 3)
('x', 'c', 1)
('x', 'c', 2)
('x', 'c', 3)
('y', 'a', 1)
('y', 'a', 2)
('y', 'a', 3)
('y', 'b', 1)
('y', 'b', 2)
('y', 'b', 3)
('y', 'c', 1)
('y', 'c', 2)
('y', 'c', 3)
('z', 'a', 1)
('z', 'a', 2)
('z', 'a', 3)
('z', 'b', 1)
('z', 'b', 2)
('z', 'b', 3)
('z', 'c', 1)
('z', 'c', 2)
('z', 'c', 3)
>>> result = product(list1, list2, list3)
>>> list(result)
[('x', 'a', 1), ('x', 'a', 2), ('x', 'a', 3), ('x', 'b', 1), ('x', 'b', 2), ('x', 'b', 3), ('x', 'c', 1), ('x', 'c', 2), ('x', 'c', 3), ('y', 'a', 1), ('y', 'a', 2), ('y', 'a', 3), ('y', 'b', 1), ('y', 'b', 2), ('y', 'b', 3), ('y', 'c', 1), ('y', 'c', 2), ('y', 'c', 3), ('z', 'a', 1), ('z', 'a', 2), ('z', 'a', 3), ('z', 'b', 1), ('z', 'b', 2), ('z', 'b', 3), ('z', 'c', 1), ('z', 'c', 2), ('z', 'c', 3)]