Clean up Qt socket notifier to avoid spurious interrupt handler calls

chrisjbillington · chrisjbillington · commit 14b531db594c · 2025-06-24T18:19:41.000+10:00
Closes #29688 Objects without a parent are not necessarily cleaned up in PyQt when their reference count reaches zero, and must be explicitly cleaned up with `deleteLater()` This prevents the notifier firing after the signal handling was supposed to have been reset to its previous state.
diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
@@ -151,8 +151,10 @@ def _allow_interrupt_qt(qapp_or_eventloop):
     """A context manager that allows terminating a plot by sending a SIGINT."""
 
     # Use QSocketNotifier to read the socketpair while the Qt event loop runs.
+    sn = None
 
     def prepare_notifier(rsock):
+        nonlocal sn
         sn = QtCore.QSocketNotifier(rsock.fileno(), QtCore.QSocketNotifier.Type.Read)
 
         @sn.activated.connect
@@ -172,6 +174,8 @@ def _may_clear_sock():
         return sn  # Actually keep the notifier alive.
 
     def handle_sigint():
+        # Ensure notifier does not outlive the event loop shutting down:
+        sn.deleteLater()
         if hasattr(qapp_or_eventloop, 'closeAllWindows'):
             qapp_or_eventloop.closeAllWindows()
         qapp_or_eventloop.quit()
