Tests hang in Python 3.14.0rc1

[musicinmybrain]

I was looking at the failure to rebuild of the python-httpx package in Fedora Rawhide, where the system Python is 3.14.0rc1, and I found that I could reproduce the problem in a virtualenv.

(Note below that I did not use the pinned versions in requirements.txt, and I did not install the brotli or zstd extras because the corresponding packages do not yet have binary wheels for Python 3.14. This is also why I needed --ignore=tests/test_decoders.py.)

$ git clone https://github.com/encode/httpx.git
$ cd httpx
$ uv venv --python 3.14
Using CPython 3.14.0rc1 interpreter at: /usr/bin/python3.14
[…]
$ . .venv/bin/activate
(httpx) $ uv pip install -e .[cli,http2,socks]
(httpx) $ uv pip install chardet 'coverage[toml]' cryptography pytest trio trio-typing trustme uvicorn
(httpx) $ pytest --ignore=tests/test_decoders.py -v
======================================== test session starts ========================================
platform linux -- Python 3.14.0rc1, pytest-8.4.1, pluggy-1.6.0 -- /home/ben/src/forks/httpx/.venv/bin/python3
cachedir: .pytest_cache
rootdir: /home/ben/src/forks/httpx
configfile: pyproject.toml
plugins: anyio-4.9.0
collected 1378 items                                                                                

tests/client/test_async_client.py::test_get[asyncio] 

This hangs indefinitely – I waited at least several minutes.

If I add --ignore=tests/client/test_async_client.py and repeat the pytest invocation, I find that some tests do pass, but there are other modules with tests that hang, too:

tests/client/test_auth.py::test_basic_auth[asyncio] PASSED                                    [  0%]
[…]
tests/client/test_auth.py::test_sync_auth PASSED                                              [  6%]
tests/client/test_client.py::test_get

With --ignore=tests/client/test_client.py, yet another hang:

[…]
tests/client/test_cookies.py::test_cookie_persistence PASSED                                  [  6%]
tests/client/test_event_hooks.py::test_event_hooks FAILED                                     [  6%]
tests/client/test_event_hooks.py::test_event_hooks_raising_exception 

Do you have any idea what might be going wrong here? Shall I open an issue?

[cclauss]

Please retry on the Python 3.14 production release.

[musicinmybrain]

I tried again just now with Python 3.14.0 final and got some failures, but no hangs:

$ git clone https://github.com/encode/httpx.git
$ cd httpx
$ uv venv --python 3.14
Using CPython 3.14.0 interpreter at: /usr/bin/python3.14
[…]
$ . .venv/bin/activate
(httpx) $ uv pip install -e .[cli,http2,socks]
(httpx) $ uv pip install chardet 'coverage[toml]' cryptography pytest trio trio-typing trustme uvicorn
(httpx) $ pytest --ignore=tests/test_decoders.py -v
[…]
========================================= FAILURES ==========================================
[…]
================================== short test summary info ==================================
SKIPPED [1] tests/client/test_auth.py:273: netrc files without a password are valid from Python >= 3.11
======================== 21 failed, 1356 passed, 1 skipped in 4.63s =========================

[mirthebeijers]

I was able to replicate the hangs. The problem is that in the test suite deprecations are marked as fatal, and uvicorn is used to set up the tests, and uvicorn generates a deprecation warning because of iscoroutinefunction() which causes test setup to 'hang' :-(

uvicorn is about to create a new release with a fix: Kludex/uvicorn#2723 👀

[cclauss]

- asyncio.iscoroutinefunction(func)
+ inspect.iscoroutinefunction(func)

[mirthebeijers]

Sure, that is part of that PR, with a little wrapper around it for compatibility. But there is also more!

• Python 3.14 has stricter requirements for event loops in background threads. The original code in httpx called server.run() which internally uses asyncio.run(), but this doesn't work properly in background threads in Python 3.14.
• asyncio.get_event_loop() deprecated: The TestServer.serve() method was using asyncio.get_event_loop() which is now more restrictive in Python 3.14.

I'll see if I can make a PR with fixes!!

[mirthebeijers]

I now created #3693