`AbstractContextManger.__enter__` should be abstract

Code sample in basedpyright playground

from contextlib import AbstractContextManager
from typing import override


class CM(AbstractContextManager[int]):
    @override
    def __exit__(self, *_): ...

with CM() as i:
    print(i + 1)

AbstractContextManger.__enter__ has a default implementation that returns self, so by making it abstract you would require implementations to provide the correct implementation. this would force a redundant implementation if the type is Self, but that is currently impossible to type anyway: https://discuss.python.org/t/self-as-typevar-default/90939

even without Self support, it is only one line of redundant code: def __enter__(self) -> Self: return self

Inizia con il basedpyright playground example e con l’AbstractContextManager stub entry point che questo esercita. Verifica in che modo l’attuale enter predefinito influisce sul controllo delle classi astratte, quindi verifica che renderlo astratto richieda un’implementazione, preservando al contempo il comportamento di tipizzazione previsto per i context manager.