使用收益递归 [英] Recursion using yield

问题描述

有没有办法混合递归和yield语句?例如，无限数生成器(使用递归)将类似于:

Is there any way to mix recursion and the yield statement? For instance, a infinite number generator (using recursion) would be something like:

def infinity(start):
    yield start
    # recursion here ...

>>> it = infinity(1)
>>> next(it)
1
>>> next(it)
2

我尝试过:

def infinity(start):
    yield start
    infinity(start + 1)

和

def infinity(start):
    yield start
    yield infinity(start + 1)

但是他们都不满足我的要求，第一个产生start后停止，第二个产生start，然后生成器，然后停止.

But none of them did what I want, the first one stopped after it yielded start and the second one yielded start, then the generator and then stopped.

注意::请知道，您可以使用while循环来做到这一点:

NOTE: Please, I know you can do this using a while-loop:

def infinity(start):
    while True:
        yield start
        start += 1

我只想知道这是否可以递归完成.

I just want to know if this can be done recursively.

推荐答案

是的，您可以这样做:

def infinity(start):
    yield start
    for x in infinity(start + 1):
        yield x

但是，一旦达到最大递归深度，就会出错.

This will error out once the maximum recursion depth is reached, though.

从Python 3.3开始，您将可以使用

Starting from Python 3.3, you'll be able to use

def infinity(start):
    yield start
    yield from infinity(start + 1)

如果仅递归地调用生成器函数而不循环或生成它，则要做的就是构建一个新的生成器，而无需实际运行函数主体或产生任何结果.

If you just call your generator function recursively without looping over it or yield from-ing it, all you do is build a new generator, without actually running the function body or yielding anything.

有关更多详细信息，请参见 PEP 380 .

See PEP 380 for further details.

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