Backport PR #16948: solution: All subclasses of LocationEvent could be used in cbook.callbacks before being fully initialized - issue 15139

QuLogic · meeseeksmachine · commit 8c7dbe1f8664 · 2020-06-09T22:16:59.000Z
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1420,14 +1420,17 @@ def __init__(self, name, canvas, x, y, button=None, key=None,
         (*x*, *y*) in figure coords ((0, 0) = bottom left)
         button pressed None, 1, 2, 3, 'up', 'down'
         """
-        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
         if button in MouseButton.__members__.values():
             button = MouseButton(button)
         self.button = button
         self.key = key
         self.step = step
         self.dblclick = dblclick
 
+        # super-init is deferred to the end because it calls back on
+        # 'axes_enter_event', which requires a fully initialized event.
+        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
+
     def __str__(self):
         return (f"{self.name}: "
                 f"xy=({self.x}, {self.y}) xydata=({self.xdata}, {self.ydata}) "
@@ -1512,8 +1515,9 @@ def on_key(event):
         cid = fig.canvas.mpl_connect('key_press_event', on_key)
     """
     def __init__(self, name, canvas, key, x=0, y=0, guiEvent=None):
-        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
         self.key = key
+        # super-init deferred to the end: callback errors if called before
+        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
 
 
 def _get_renderer(figure, print_method, *, draw_disabled=False):
