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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: TimerAsyncio does not work with Python 3.14","articleBody":"### Bug summary\n\nThe `test_backends_interactive.py::test_webagg` test is failing on Python 3.14, because the implementation of `TimerAsyncio` uses `asyncio.ensure_future` when there is no current event loop. `asyncio.ensure_future` calls [`asyncio.get_event_loop()`](https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.get_event_loop) when a loop is not given, and that raises a [RuntimeError](https://docs.python.org/3/library/exceptions.html#RuntimeError) if there is no current event loop.\n\n### Code for reproduction\n\nRun the matplotlib testsuite on Python 3.14\n\n### Actual outcome\n\n```\n=================================== FAILURES ===================================\n_________________________________ test_webagg __________________________________\n[gw28] linux -- Python 3.14.2 /build/python-matplotlib/src/matplotlib/test-env/bin/python\n\n    @pytest.mark.skipif('TF_BUILD' in os.environ,\n                        reason=\"this test fails an azure for unknown reasons\")\n    @pytest.mark.skipif(sys.platform == \"win32\", reason=\"Cannot send SIGINT on Windows.\")\n    def test_webagg():\n        pytest.importorskip(\"tornado\")\n        proc = subprocess.Popen(\n            [sys.executable, \"-c\",\n             inspect.getsource(_test_interactive_impl)\n             + \"\\n_test_interactive_impl()\", \"{}\"],\n            env={**os.environ, \"MPLBACKEND\": \"webagg\", \"SOURCE_DATE_EPOCH\": \"0\"})\n        url = f'http://{mpl.rcParams[\"webagg.address\"]}:{mpl.rcParams[\"webagg.port\"]}'\n        timeout = time.perf_counter() + _test_timeout\n        try:\n            while True:\n                try:\n                    retcode = proc.poll()\n                    # check that the subprocess for the server is not dead\n\u003e                   assert retcode is None\nE                   assert 1 is None\n\ntest-env/lib/python3.14/site-packages/matplotlib/tests/test_backends_interactive.py:493: AssertionError\n----------------------------- Captured stderr call -----------------------------\nTraceback (most recent call last):\n  File \"\u003cstring\u003e\", line 83, in \u003cmodule\u003e\n    _test_interactive_impl()\n    ~~~~~~~~~~~~~~~~~~~~~~^^\n  File \"\u003cstring\u003e\", line 69, in _test_interactive_impl\n    fig.savefig(result, format='png')\n    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/figure.py\", line 3490, in savefig\n    self.canvas.print_figure(fname, **kwargs)\n    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 2186, in print_figure\n    result = print_method(\n        filename,\n    ...\u003c3 lines\u003e...\n        bbox_inches_restore=_bbox_inches_restore,\n        **kwargs)\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 2042, in \u003clambda\u003e\n    print_method = functools.wraps(meth)(lambda *args, **kwargs: meth(\n                                                                 ~~~~^\n        *args, **{k: v for k, v in kwargs.items() if k not in skip}))\n        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backends/backend_agg.py\", line 481, in print_png\n    self._print_pil(filename_or_obj, \"png\", pil_kwargs, metadata)\n    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backends/backend_agg.py\", line 429, in _print_pil\n    FigureCanvasAgg.draw(self)\n    ~~~~~~~~~~~~~~~~~~~~^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backends/backend_agg.py\", line 382, in draw\n    self.figure.draw(self.renderer)\n    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/artist.py\", line 94, in draw_wrapper\n    result = draw(artist, renderer, *args, **kwargs)\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/artist.py\", line 71, in draw_wrapper\n    return draw(artist, renderer)\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/figure.py\", line 3264, in draw\n    DrawEvent(\"draw_event\", self.canvas, renderer)._process()\n    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 1189, in _process\n    self.canvas.callbacks.process(self.name, self)\n    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/cbook.py\", line 366, in process\n    self.exception_handler(exc)\n    ~~~~~~~~~~~~~~~~~~~~~~^^^^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/cbook.py\", line 110, in _exception_printer\n    raise exc\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/cbook.py\", line 361, in process\n    func(*args, **kwargs)\n    ~~~~^^^^^^^^^^^^^^^^^\n  File \"\u003cstring\u003e\", line 65, in \u003clambda\u003e\n    fig.canvas.mpl_connect(\"draw_event\", lambda event: timer.start())\n                                                       ~~~~~~~~~~~^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/_api/deprecation.py\", line 382, in wrapper\n    return func(*inner_args, **inner_kwargs)\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 1069, in start\n    self._timer_start()\n    ~~~~~~~~~~~~~~~~~^^\n  File \"/build/python-matplotlib/src/matplotlib/test-env/lib/python3.14/site-packages/matplotlib/backends/backend_webagg_core.py\", line 139, in _timer_start\n    self._task = asyncio.ensure_future(\n                 ~~~~~~~~~~~~~~~~~~~~~^\n        self._timer_task(max(self.interval / 1_000., 1e-6))\n        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n    )\n    ^\n  File \"/usr/lib/python3.14/asyncio/tasks.py\", line 730, in ensure_future\n    loop = events.get_event_loop()\n  File \"/usr/lib/python3.14/asyncio/events.py\", line 715, in get_event_loop\n    raise RuntimeError('There is no current event loop in thread %r.'\n                       % threading.current_thread().name)\nRuntimeError: There is no current event loop in thread 'MainThread'.\n\u003csys\u003e:0: RuntimeWarning: coroutine 'TimerAsyncio._timer_task' was never awaited\n=========================== short test summary info ============================\nFAILED test-env/lib/python3.14/site-packages/matplotlib/tests/test_backends_interactive.py::test_webagg - assert 1 is None\n```\n\n### Expected outcome\n\nNo test failure\n\n### Additional information\n\n_No response_\n\n### Operating system\n\nArch\n\n### Matplotlib Version\n\n3.10.8\n\n### Matplotlib Backend\n\n_No response_\n\n### Python version\n\n3.14.2\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nNone","author":{"url":"https://github.com/lahwaacz","@type":"Person","name":"lahwaacz"},"datePublished":"2025-12-31T10:46:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/30917/matplotlib/issues/30917"}