Clear nonlocal socket notifier variable on cleanup

chrisjbillington · chrisjbillington · commit 098532b3cf2f · 2025-06-25T15:46:12.000+10:00
Although in normal operation this shouldn't matter (it will go out of
scope anyway), it would be better if any future bugs here raised a
`TypeError` upon encountering `sn` being `None` instead of experiencing
an ungraceful shutdown due to SIGABRT upon attempting to access a
no-longer-existing C++ object.
diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
@@ -175,11 +175,13 @@ def _may_clear_sock():
 
     def handle_sigint():
         # Ensure notifier does not outlive the event loop shutting down:
+        nonlocal sn
         sn.deleteLater()
         QtCore.QCoreApplication.sendPostedEvents(sn, QtCore.QEvent.Type.DeferredDelete)
         if hasattr(qapp_or_eventloop, 'closeAllWindows'):
             qapp_or_eventloop.closeAllWindows()
         qapp_or_eventloop.quit()
+        sn = None
 
     return _allow_interrupt(prepare_notifier, handle_sigint)
 
