FIX: be very paranoid about checking what the current canvas is

tacaswell · tacaswell · commit 54db9763804a · 2023-03-29T16:18:54.000-04:00
closes #25572
diff --git a/lib/matplotlib/tests/test_widgets.py b/lib/matplotlib/tests/test_widgets.py
@@ -1740,3 +1740,14 @@ def test_MultiCursor(horizOn, vertOn):
         assert l.get_xdata() == (.5, .5)
     for l in multi.hlines:
         assert l.get_ydata() == (.25, .25)
+
+
+def test_parent_axes_removal():
+
+    fig, ax = plt.subplots(1, 1)
+
+    radio = widgets.RadioButtons(ax, ['1', '2'], 0)
+
+    ax.remove()
+    with io.BytesIO() as out:
+        fig.savefig(out, format='raw')
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -104,7 +104,15 @@ def _changed_canvas(self):
            True if the canvas has been changed.
 
         """
-        return self.canvas is not self.ax.figure.canvas
+        # no canvas, something is very fishy
+        if self.canvas is None:
+            return True
+        # self.ax.figure.canvas but very defensively, can got to odd states if the
+        # the widget or the parent Axes is removed from the Figure
+        parent_canvas = getattr(
+            getattr(getattr(self, 'ax', None), 'figure', None), 'canvas', None
+        )
+        return self.canvas is not parent_canvas
 
 
 class AxesWidget(Widget):
