I think it's a micro-optimization that's probably not worth it for most
code and more likely to occasionally disappoint people who are using the
debugger.
Once we have a JIT mode or other super-optimization mode it can be done.
On Tue, Oct 20, 2020 at 7:32 AM Serhiy Storchaka <storch...@gmail.com>
wrote:
> It is common to use _ as a placeholder for variable whose value is not
> used. For example:
>
> for _ in range(n)
> head, _, tail = name.partition(':')
> first, *_, last = items
>
> I though about optimizing out unnecessary assignments. Actually I wrote
> a patch half year ago and tested it. It did not add much to performance,
> and did not reduce the bytecode, so I ccoled down to him and put it off.
> Later PEP 622 was declared the use of _ in pattern matching, so I was
> waiting for what it would come to. And now PEP 640 is created to solve
> the same problem.
>
> My patch was too conservative. It was limited to local variables and
> underscored names. For global variables we can't determine if the
> variable is not used. And eliminating unused non-underscored variables
> breaks too many tests (mainly for debugger, tracing, etc).
>
> I was not sure whether it should be limited to underscored names or just
> '_' (I seen also uses of '__' as a drop out variable in wild).
>
> Maybe we can extend this to global '_'. Global '_' is used as a holder
> for the last result in REPL and as an alias to gettext (this is the
> reason of PEP 640), but none of them is actually set in the assignment
> statement. You can use `globals()['_'] = ...` or `globals().update({'_':
> ...})` or `sys.modules[__name__]._ = ...` to set global '_'.
>
> 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?
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*Pronouns: he/him **(why is my pronoun here?)*
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