Python 嵌套生成器不工作

Question

我正在练习生成器，我想知道为什么下面的代码不打印 16 对而只打印 4 对。

def range_generator_function(my_range):
    for i in my_range:
        yield i

gen1=range_generator_function(range(1,5))
gen2=range_generator_function(range(1,5))

def pairs_generator_function(gen1,gen2):
    for it1 in gen1:
        for it2 in gen2:
            yield [it1,it2]

my_gen = pairs_generator_function(gen1,gen2)

for it in my_gen:
    print(it)

输出是

[1, 1]
[1, 2]
[1, 3]
[1, 4]

虽然我期望的输出是

[1, 1]
[1, 2]
[1, 3]
[1, 4]
[2, 1]
[2, 2]
[2, 3]
[2, 4]
[3, 1]
[3, 2]
[3, 3]
[3, 4]
[4, 1]
[4, 2]
[4, 3]
[4, 4]

Answer 1

实际输出是正确的。您的 gen2 实例已被第一个内部循环完全耗尽:

def pairs_generator_function(gen1,gen2):
    for it1 in gen1:
        for it2 in gen2:  # <--- this consumes gen2
            yield [it1,it2]

在随后的迭代中，再次迭代 gen2 是空的。