Backport PR #16330: Clearer signal handling

anntzer · meeseeksmachine · commit a01ca175deae · 2020-01-28T16:55:07.000Z
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -1092,11 +1092,12 @@ def trigger_manager_draw(manager):
     def mainloop():
         old_signal = signal.getsignal(signal.SIGINT)
         # allow SIGINT exceptions to close the plot window.
-        if old_signal:
+        is_python_signal_handler = old_signal is not None
+        if is_python_signal_handler:
             signal.signal(signal.SIGINT, signal.SIG_DFL)
         try:
             qApp.exec_()
         finally:
             # reset the SIGINT exception handler
-            if old_signal:
+            if is_python_signal_handler:
                 signal.signal(signal.SIGINT, old_signal)
