[Python-Dev] Tricky way of of creating a generator via a comprehension expression

[Ivan Levkivskyi]

22 Лис 2017 22:19 "Ethan Furman" <ethan at stoneleaf.us> пише:

On 11/22/2017 11:01 AM, Ivan Levkivskyi wrote:

I think how to formulate these rules more "precisely" so that they will be
> all consistent even if there is a
> `yield` inside.
> The key idea is that neither comprehensions nor generator expressions
> should create a function scope surrounding the
> `expr` in (expr for ind in iterable) and [expr for ind in iterable].
> (this still can be some hidden implementation detail)
>
> So as Serhiy proposed in one of his first posts any comprehensions and
> generator expressions with `yield` are not valid
> outside functions.
> If such comprehension or generator expression is inside a function, then
> it makes it a generator, and all the `yield`s
>
> are yielded from that generator, for example:
>

Whether it's inside or outside a function should be irrelevant -- a
comprehension / generator expression should have no influence on the type
of the resulting function (and at least synchronous comprehensions /
generator expressions should be able to live outside of a function).


def fun_gen():
>      return list((yield i) for i in range(3))
>

The return says it's returning a list, so that's what it should be returning


def f():
    yield 1
    return list()

Here return also says it should return a list, so this is not an argument.
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