Context manager support for `contextvars.Context`

Feature or enhancement

I would like to add __enter__ and __exit__ methods to contextvars.Context such that these two are mostly equivalent:

contextvars.copy_context().run(do_something_interesting)

and:

with contextvars.copy_context():
    do_something_interesting()

Pitch

This makes it possible to combine Context enter/exit with other context managers:

import contextlib
import contextvars

@contextlib.contextmanager
def foo():
    with contextvars.copy_context():
        set_some_context_vars()
        yield

My personal motivating interest is controlling ContextVar values in pytest fixtures. For example:

import contextvars
import pytest
import module_under_test

@pytest.fixture
def clean_slate():
    with contextvars.copy_context():
        module_under_test._internal_state_context_var.set(None)
        yield

def test_foo(clean_slate):
    assert not module_under_test.is_initialized()

Previous discussion

https://stackoverflow.com/q/59264158

Linked PRs

• gh-124773
• gh-124776
• gh-99634

Empieza leyendo la documentación de contextvars.Context y los ejemplos de equivalencia del issue; después, revisa los PRs enlazados gh-124773, gh-124776 y gh-99634 antes de comenzar. Se considera terminado cuando Context admite el uso solicitado como gestor de contexto y el comportamiento coincide con el ejemplo existente de run(), incluida la composición con otros gestores de contexto.