标准语法
itertools.product(*iterables[, repeat])
含义
Cartesian product of input iterables.
Roughly equivalent to nested for-loops in a generator expression. For example, product(A, B) returns the same as ((x,y) for x in A for y in B).
The nested loops cycle like an odometer with the rightmost element advancing on every iteration. This pattern creates a lexicographic ordering so that if the input’s iterables are sorted, the product tuples are emitted in sorted order.
To compute the product of an iterable with itself, specify the number of repetitions with the optional repeat keyword argument. For example, product(A, repeat=4) means the same as product(A, A, A, A).
大致的意思呢就是返回可迭代对象的笛卡尔积，可选参数repeat指定重复次数。若要计算可迭代对象与自身的乘积，请使用可选的repeat关键字参数指定重复次数。例如，乘积(A, repeat=4)与乘积(A, A, A, A)相同。
代码
def product(*args, **kwds):
# product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
# product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
pools = map(tuple, args) * kwds.get('repeat', 1)
result = [[]]
for pool in pools:
result = [x+[y] for x in result for y in pool]
for prod in result:
yield tuple(prod)