[New-bugs-announce] [issue39754] update_one_slot() does not inherit sq_contains and mp_subscript if they are explictly declared

[Marco Sulla]

New submission from Marco Sulla <launchpad.net at marco.sulla.e4ward.com>:

I noticed that `__contains__()` and `__getitem__()` of subclasses of `dict` are much slower. I asked why on StackOverflow, and an user seemed to find the reason.

The problem for him/her is that `dict` implements directly `__contains__()` and `__getitem__()`. Usually, `sq_contains` and `mp_subscript` are wrapped to implement `__contains__()` and `__getitem__()`, but this way `dict` is a little faster, I suppose.

The problem is that `update_one_slot()` searches for the wrappers. If it does not find them, it does not inherit the `__contains__()` and `__getitem__()` of the class, but create a `__contains__()` and `__getitem__()` functions that do an MRO search and call the superclass method. This is why `__contains__()` and `__getitem__()` of `dict` subclasses are slower.


Is it possible to modify `update_one_slot()` so that, if no wrapper is found, the explicit implementation is inherited?

SO answer: https://stackoverflow.com/a/59914459/1763602

----------
components: C API
messages: 362662
nosy: Marco Sulla
priority: normal
severity: normal
status: open
title: update_one_slot() does not inherit sq_contains and mp_subscript if they are explictly declared
type: performance
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39754>
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