发电机可以使用一次以上吗? [英] Can generator be used more than once?

问题描述

这是我的代码，其中定义了两个生成器:

This is my piece of code with two generators defined:

one_line_gen = (x for x in range(3))

def three_line_gen():
    yield 0
    yield 1
    yield 2

执行时:

for x in one_line_gen:
    print x

for x in one_line_gen:
    print x

结果符合预期:

0
1
2

但是，如果我执行:

for x in three_line_gen():
    print x

for x in three_line_gen():
    print x

结果是:

0
1
2
0
1
2

为什么?我以为任何生成器只能使用一次.

Why? I thought any generator can be used only once.

推荐答案

three_line_gen不是生成器，它是一个函数.调用它时返回的是一个生成器，每次调用时都会生成一个全新的生成器.每次您这样插入括号:

three_line_gen is not a generator, it's a function. What it returns when you call it is a generator, a brand new one each time you call it. Each time you put parenthesis like this:

three_line_gen()

这是一个需要迭代的全新生成器.但是，如果您要先这样做

It is a brand new generator to be iterated on. If however you were to first do

mygen = three_line_gen()

并遍历mygen两次，第二次将失败，如您所愿.

and iterate over mygen twice, the second time will fail as you expect.

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