Backport PR #16028: Prevent FigureCanvasQT_draw_idle recursively calling itself.

Kojoley · meeseeksmachine · commit e6ffa5dd632f · 2019-12-29T20:04:02.000Z
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -498,17 +498,16 @@ def draw_idle(self):
             QtCore.QTimer.singleShot(0, self._draw_idle)
 
     def _draw_idle(self):
-        if self.height() < 0 or self.width() < 0:
-            self._draw_pending = False
         if not self._draw_pending:
             return
+        self._draw_pending = False
+        if self.height() < 0 or self.width() < 0:
+            return
         try:
             self.draw()
         except Exception:
             # Uncaught exceptions are fatal for PyQt5, so catch them instead.
             traceback.print_exc()
-        finally:
-            self._draw_pending = False
 
     def drawRectangle(self, rect):
         # Draw the zoom rectangle to the QPainter.  _draw_rect_callback needs
