20.10.20 20:13, Steven D'Aprano пише:
> On Tue, Oct 20, 2020 at 05:30:54PM +0300, Serhiy Storchaka wrote:
>
>> I do not want to create tens of alternate PEPs with minor variations,
>> and this issue is not worth a PEP. What is your opinion about this? Is
>> it worth to include such optimization? For what kind of variables should
>> it be applied? Should it include global '_'? Should it be merely an
>> optimization (maybe controlled by the -O option) or change in the language?
>
> Assuming that this actually has a benefit, in either speed or memory,
> how about this?
And this is a large IF.
> 1. Only eliminate local variables, never globals.
>
> 2. By default, only variables with a leading underscore are eliminated.
> This will(?) avoid breaking tests for the debugger etc. that you
> mentioned.
It is actually what my patch does.
> 3. Under -O, allow more aggressive optimization that eliminates
> non-underscore variables too.
It is easy to add, but as Guido noted it will break the code that uses
locals(). I though about eliminating underscore variables only with -O.
It would make the feature safer, but even less useful.
> 4. This is an implementation feature, not a language promise. Other
> interpreters do not have to follow.
It is a question about which I am not sure.
> 5. To be clear, variables are only eliminated if they are assigned to,
> but never written to:
Yes. And for implementation simplification "del" counts as the use of
the variable. So _ is not eliminated in the following code:
a, *_ = foo()
del _
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