MNT: project Qt backends from recursive draws

tacaswell · tacaswell · commit 5a6ae8135643 · 2017-10-22T15:22:58.000-04:00
This does not prevent the recursion, which may segfault Qt, but prevents it from infinitely recursing if Qt does not crash. Closes #9406
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -140,18 +140,22 @@ def draw_idle(self):
             QtCore.QTimer.singleShot(0, self.__draw_idle_agg)
 
     def __draw_idle_agg(self, *args):
+        # if nothing to do, bail
         if not self._agg_draw_pending:
             return
+        # we have now tried this function at least once, do not run
+        # again until re-armed.  Doing this here rather than after
+        # protects against recursive calls triggered through self.draw
+        self._agg_draw_pending = False
+        # if negative size, bail
         if self.height() < 0 or self.width() < 0:
-            self._agg_draw_pending = False
             return
         try:
+            # actually do the drawing
             self.draw()
         except Exception:
             # Uncaught exceptions are fatal for PyQt5, so catch them instead.
             traceback.print_exc()
-        finally:
-            self._agg_draw_pending = False
 
     def blit(self, bbox=None):
         """Blit the region in bbox.
