Context manager support for `contextvars.Context`

[rhansen]

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-124872: Refine contextvars documentation #124773
• gh-124872: Replace enter/exit events with "switched" #124776
• gh-99633: Add context manager support to contextvars.Context #99634

[gvanrossum]

The idea should probably be reviewed by @1st1.

[rhansen]

Friendly ping @1st1

[apostolos-geyer]

+1

[gvanrossum]

Maybe someone could contribute a PR?