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Deprecation in Python 3.14 will break python -m textual and App.run() #5797

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DavidCEllis opened this issue May 12, 2025 · 2 comments · May be fixed by #5799
Open

Deprecation in Python 3.14 will break python -m textual and App.run() #5797

DavidCEllis opened this issue May 12, 2025 · 2 comments · May be fixed by #5799

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@DavidCEllis
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The bug

Python 3.14 removes the ability to use get_event_loop to implicitly create a loop. You can get the same failure with -Werror on Python 3.13.

This means python -m textual errors in 3.14 and App.run() will fail if not given a loop:

$ python -m textual
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\ducks\Source\ducktools-pytui\.venv_textualtest\Lib\site-packages\textual\__main__.py", line 5, in <module>
    app.run()
    ~~~~~~~^^
  File "C:\Users\ducks\Source\ducktools-pytui\.venv_textualtest\Lib\site-packages\textual\app.py", line 2154, in run
    event_loop = asyncio.get_event_loop() if loop is None else loop
                 ~~~~~~~~~~~~~~~~~~~~~~^^
  File "C:\Users\ducks\AppData\Local\Python\pythoncore-3.14-64\Lib\asyncio\events.py", line 718, in get_event_loop
    raise RuntimeError('There is no current event loop in thread %r.'
                       % threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'MainThread'.

It looks like the logic that defended against this was removed recently: 4e4e2a3
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@graingert
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Dup of #5788

@graingert graingert linked a pull request May 13, 2025 that will close this issue
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@graingert @DavidCEllis