Question

在以下代码中：

import heapq

nums = [1,2,3]
result = [set([])]
bases = []

for n in nums:
    bases.append(set([n]))       # Now bases is [set([1]), set([2]), set([3])]

def gen (base):
    for r in result:
        if base != r:
            yield base | r       # It yields set([]) unions base

itr1 = iter(map(gen, bases))
itr2 = heapq.merge(*map(gen, bases))

为什么itr1是迭代器的迭代器，但是itr2是集合的迭代器？如下所示：

for i in itr1:
    print i                      #<generator object gen at 0x1028adcd0> 
                                 #<generator object gen at 0x1028add20> 
                                 #<generator object gen at 0x1028d5730>

for i in itr2:
    print i,                     #set([3]) set([2]) set([1])

Answer 1

您是否尝试过更改：

itr1 = iter(map(gen, bases))
itr2 = heapq.merge(*map(gen, bases))

为：

itr1 = iter(map(gen, bases))
itr2 = iter(heapq.merge(*map(gen, bases)))

为什么`heapq.merge（some_lists_of_iterators）`不返回迭代器的迭代器？

1 个答案: