On Thu, Mar 12, 2020 at 03:02:28PM -0000, Eric Wieser wrote:
> TL;DR: should we make `del x` an expression that returns the value of `x`.
>
> ## Motivation
>
> I noticed yesterday that `itertools.combinations` has an optimization
> for when the returned tuple has no remaining ref-counts, and reuses it
> - namely, the following code:
>
> >>> for v in itertools.combinations([1, 2, 3], 1):
> ... print(id(v))
> ... del v # without this, the optimization can't take place
> 2500926199840
> 2500926199840
> 2500926199840
[...]
> My suggestion would be to make `del x` an expression, with semantics
> "unbind the name `x`, and evaluate to its value".
> This would allow:
>
> >>> [id(del v) for v in itertools.combinations([1, 2, 3], 1)]
> [2500926200992, 2500926200992, 2500926200992]
Pity that locals() is so weird, because this works fine in module level
code, but not inside comprehensions or functions:
py> for v in combinations([1, 2, 3], 1):
... print(id(locals().pop('v')))
...
3083202636
3083202636
3083202636
Mind you, I think that the cost of calling locals().pop is going to
outweigh any hypothetical saving you get from reusing the object.
--
Steven
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