update_one_slot() does not inherit sq_contains and mp_subscript if they are explictly declared

[Marco-Sulla]

BPO	39754
Nosy	@benjaminp, @Marco-Sulla

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-02-26.19:09:15.608>
created_at = <Date 2020-02-25.20:17:09.547>
labels = ['expert-C-API', '3.9', 'performance']
title = 'update_one_slot() does not inherit sq_contains and mp_subscript if they are explictly declared'
updated_at = <Date 2020-02-26.19:09:15.607>
user = 'https://github.com/Marco-Sulla'

bugs.python.org fields:

activity = <Date 2020-02-26.19:09:15.607>
actor = 'Marco Sulla'
assignee = 'none'
closed = True
closed_date = <Date 2020-02-26.19:09:15.608>
closer = 'Marco Sulla'
components = ['C API']
creation = <Date 2020-02-25.20:17:09.547>
creator = 'Marco Sulla'
dependencies = []
files = []
hgrepos = []
issue_num = 39754
keywords = []
message_count = 2.0
messages = ['362662', '362677']
nosy_count = 2.0
nosy_names = ['benjamin.peterson', 'Marco Sulla']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue39754'
versions = ['Python 3.9']

[Marco-Sulla]

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

[benjaminp]

See also bpo-34396.