相关疑难解决方法(0)

我希望以下片段给我一个迭代器,从两个输入迭代的笛卡尔乘积产生对:

$ python
Python 2.7.1+ (r271:86832, Apr 11 2011, 18:13:53) 
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import itertools
>>> one = xrange(0, 10**9)
>>> two = (1,)
>>> prods = itertools.product(one, two)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
MemoryError

相反,我得到了一个MemoryError.但我认为itertools.product没有将中间结果存储在内存中,那么是什么导致了MemoryError？

该文件说,笛卡尔积函数

the actual implementation does not build up intermediate results in memory.

如何用发电机做到这一点？有人能给我看一个2个发生器的有限内存消耗的例子吗？

使用pythons itertools,我想在一堆列表的所有排列的外积上创建一个迭代器.一个明确的例子:

import itertools
A = [1,2,3]
B = [4,5]
C = [6,7]

for x in itertools.product(itertools.permutations(A),itertools.permutations(B),itertools.permutations(C)):
    print x

虽然这有效,但我想将其推广到任意列表列表.我试过了:

for x in itertools.product(map(itertools.permutations,[A,B,C])):
    print x

但它并没有按照我的意图行事.预期的产出是:

((1, 2, 3), (4, 5), (6, 7))
((1, 2, 3), (4, 5), (7, 6))
((1, 2, 3), (5, 4), (6, 7))
((1, 2, 3), (5, 4), (7, 6))
((1, 3, 2), (4, 5), (6, 7))
((1, 3, 2), (4, 5), (7, 6))
((1, 3, 2), (5, 4), (6, 7))
((1, 3, 2), …