Python 3.12.4 seg faulting when running pytest with mpl

[bje-]

Crash report

What happened?

This test file causes Python to seg fault when run with python3.12 -m pytest test_example.py:

import pytest
import unittest
import matplotlib.pyplot as plt

class TestUtils(unittest.TestCase):

    @pytest.mark.mpl_image_compare
    def test_figure_1(self):
        return plt.figure()

I have run it under GDB and got the following backtrace:

Thread 1 "python3.12" received signal SIGSEGV, Segmentation fault.
0x00000000005333f0 in _PyInterpreterState_GET () at ../Include/internal/pycore_pystate.h:133
(gdb) bt
#0  0x00000000005333f0 in _PyInterpreterState_GET () at ../Include/internal/pycore_pystate.h:133
#1  get_state () at ../Objects/obmalloc.c:866
#2  _PyObject_Free (p=0x20bf0b0, ctx=0x0) at ../Objects/obmalloc.c:1850
#3  PyMem_Free (ptr=0x20bf0b0) at ../Objects/obmalloc.c:732
#4  0x00007fffe5921839 in sip_api_free (mem=<optimised out>) at ../../../../sip/siplib/siplib.c:2162
#5  0x00007fffe591d61d in sipOMFinalise (om=om@entry=0x7fffe593fec0 <cppPyMap>)
    at ../../../../sip/siplib/objmap.c:69
#6  0x00007fffe5921a2f in finalise () at ../../../../sip/siplib/siplib.c:2064
#7  0x00000000004630c1 in call_ll_exitfuncs (runtime=<optimised out>) at ../Python/pylifecycle.c:3046
#8  Py_FinalizeEx () at ../Python/pylifecycle.c:2005
#9  0x0000000000657a9e in Py_RunMain () at ../Modules/main.c:711
#10 0x0000000000610acd in Py_BytesMain (argc=<optimised out>, argv=<optimised out>) at ../Modules/main.c:763
#11 0x00007ffff7c29d90 in __libc_start_call_main
     (main=main@entry=0x610a10 <main>, argc=argc@entry=4, argv=argv@entry=0x7fffffffe2b8)
    at ../sysdeps/nptl/libc_start_call_main.h:58
#12 0x00007ffff7c29e40 in __libc_start_main_impl
     (main=0x610a10 <main>, argc=4, argv=0x7fffffffe2b8, init=<optimised out>, fini=<optimised out>, rtld_fini=<optimised out>, stack_end=0x7fffffffe2a8) at ../csu/libc-start.c:392
#13 0x0000000000610945 in _start ()

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.12.4 (main, Jun 12 2024, 16:49:51) [GCC 11.4.0]

[mdboom]

I can't reproduce this myself, fwiw (on Debian Linux). Seeing sip_api_free in the traceback makes me think this is related to PyQt. Does using a different matplotlib backend resolve the issue? Is it possible to create the crash on a simple PyQt example application alone (without matplotlib and pytest in the mix?)

[bje-]

Thanks for your help. I've managed to remove pytest from the picture with just this:

>>> import matplotlib.pyplot as plt
>>> plt.figure()
<Figure size 640x480 with 0 Axes>
>>> 
Segmentation fault (core dumped)

I'll try a different Matplotlib backend as you suggest.

[bje-]

I switched to the PDF backend and the segfault goes away. The default backend is:

>>> import matplotlib
>>> matplotlib.get_backend()
'WxAgg'

[bje-]

This tiny wxPython test case crashes once the main window is closed. I am using wxPython 4.1.2 installed via pip.

import wx
app = wx.App()
frm = wx.Frame(None, title="Hello World")
frm.Show()
app.MainLoop()

[bje-]

Here's the bug: wxWidgets/Phoenix#2455

Not a Python core bug, quite obviously, so closing.