为什么我不能将收益与回报一起使用?

Why can#39;t I use yield with return?(为什么我不能将收益与回报一起使用?)

问题描述

我希望您考虑以下代码:

I would like you to consider the following code:

def func(alist):
    if len(alist) == 1:
        return arg * 2
    for item in alist:
        yield item * 2

当我运行它时，我得到了这个错误:

When I run it, I get this error:

SyntaxError: 'return' with argument inside generator

现在，我意识到我无法做到这一点.但是，我想知道为什么.导致 Python 抛出 SyntaxError 的幕后究竟发生了什么?

Now, I realize that I cannot do this. However, I would like to know why. What exactly is going on behind the scenes that is causing Python to throw the SyntaxError?

推荐答案

Python 必须在字节码编译时判断一个函数是否是生成器.这是因为生成器的语义表明生成器函数中的任何代码都不会在第一次 next 调用之前运行；生成器函数返回一个生成器迭代器，当调用 next 时，它会运行生成器代码.因此，Python 无法通过运行一个函数来决定它是否应该是生成器，直到它遇到 yield 或 return；相反，函数中存在 yield 表明该函数是生成器.

Python has to decide whether a function is a generator at bytecode compilation time. This is because the semantics of generators say that none of the code in a generator function runs before the first next call; the generator function returns a generator iterator that, when next is called, runs the generator code. Thus, Python can't decide whether a function should be a generator or not by running it until it hits a yield or a return; instead, the presence of a yield in a function signals that the function is a generator.

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