[Python-ideas] PEP 572: Statement-Local Name Bindings

[Chris Angelico]

On Thu, Mar 1, 2018 at 2:16 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
> 28.02.18 16:56, Chris Angelico пише:
>>>>>
>>>>>       def g():
>>>>>           for x in range(5):
>>>>>               y = f(x)
>>>>>               yield [y, y]
>>>>>       stuff = list(g)
>>>>
>>>>
>>>>
>>>> You're not the first to mention this, but I thought it basically
>>>> equivalent to the "expand into a loop" form. Is it really beneficial
>>>> to expand it, not just into a loop, but into a generator function that
>>>> contains a loop?
>>>
>>>
>>>
>>> It is slightly faster (if the list is not too small). It doesn't leak a
>>> temporary variable after loop. And in many cases you don't need a list,
>>> an
>>> iterator would work as well. In these cases it is easy to just drop
>>> calling
>>> list().
>>
>>
>> Doesn't leak a temporary? In Python 3, the list comp won't leak
>> anything, but the function is itself a temporary variable with
>> permanent scope. You're right about the generator being sufficient at
>> times, but honestly, if we're going to say "maybe you don't need the
>> same result", then all syntax questions go out the window :D
>
>
> Explicit for loop leaks variables x and y after the loop. They can hold
> references to large objects. The generator function itself doesn't hold
> references to the proceeded data.
>

Oh, gotcha. Yeah. Will add that as another example.

ChrisA