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

[Nick Coghlan]

On 23 November 2017 at 14:36, Greg Ewing <greg.ewing at canterbury.ac.nz>
wrote:

> Paul Moore wrote:
>
>> 3. List comprehensions are the same as list(the equivalent generator
>> expression).
>>
>
> I don't think that's ever been quite true -- there have
> always been odd cases such as what happens if you
> raise StopIteration in list(generator_expression).
>
> To my mind, these equivalences have never been intended
> as exact descriptions of the semantics, but just a way
> of quickly getting across the general idea. Further
> words are needed to pin down all the fine details.
>

Getting the name resolution to be identical was definitely one of my goals
when working on the Python 3 comprehension scoping changes.

The fact that implicit scopes and yield expressions interact strangely was
just a pre-existing oddity from when PEP 342 was first implemented (and one
we were able to avoid for async/await by retaining the same "await is only
permitted in async comprehensions" constraint that exists for explicit
scopes).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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