Python中的生成器和for循环 [英] Generators and for loops in Python

问题描述

所以我有一个生成器函数，看起来像这样.

So I have a generator function, that looks like this.

def generator():
    while True:
        for x in range(3):
            for j in range(5):
                yield x

加载此函数并多次调用"next"后，我希望它会产生值

After I load up this function and call "next" a bunch of times, I'd expect it to yield values

0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 0 0 0 0 0 ...

但是，它总是一直产生0.为什么会这样?

But instead it just yields 0 all the time. Why is that?

>>> execfile("test.py")
>>> generator
<function generator at 0x10b6121b8>
>>> generator().next()
0
>>> generator().next()
0
>>> generator().next()
0
>>> generator().next()
0
>>> generator().next()
0
>>> generator().next()
0
>>> generator().next()
0

推荐答案

generator()初始化新的生成器对象:

generator() initializes new generator object:

In [4]: generator() is generator() # Creating 2 separate objects
Out[4]: False

然后generator().next()从新创建的生成器对象(在您的情况下为 0 )获取第一个值.

Then generator().next() gets the first value from the newly created generator object (0 in your case).

您应该致电generator一次:

In [5]: gen = generator() # Storing new generator object, will reuse it

In [6]: [gen.next() for _ in range(6)] # Get first 6 values for demonstration purposes
Out[6]: [0, 0, 0, 0, 0, 1]

注意: generator.next 已从Python 3中删除( PEP 3114 )-使用 next函数代替:

Note: generator.next was removed from Python 3 (PEP 3114) - use the next function instead:

In [7]: next(gen)
Out[7]: 1

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