warnings: adding new filter resets prior existing "once" filters

Bug report

Bug description:

If a filter is defined with action="once", the occurrence tracking is reset each time a new filter is defined. This can override the ability to effectively use action="once" if the filter manipulation occurs in a library which the user cannot control (e.g. matplotlib).

For example, the following code will only output a warning once (i.e. works as intended):

import warnings

warnings.filterwarnings("once", "test warning", UserWarning)
warnings.warn("test warning", UserWarning)
warnings.warn("test warning", UserWarning)

However, simply inserting an unrelated filter prior to the second warning will cause both to be output:

warnings.filterwarnings("once", "test warning", UserWarning)
warnings.warn("test warning", UserWarning)

warnings.filterwarnings("ignore", "something unrelated")
warnings.warn("test warning", UserWarning)

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-153697

Commencez par le reproducer de warnings.filterwarnings et warnings.warn présent dans l’issue, puis localisez l’implémentation de warnings et ses tests dans CPython. Le travail est terminé lorsque l’ajout d’un filtre sans rapport ne réinitialise plus le suivi des occurrences d’un filtre existant avec action="once" ; gh-153697 est déjà associé à cette issue.