Merge pull request matplotlib#25573 from tacaswell/fix_removed_widget_axes

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

Author: timhoffm

lib/matplotlib/tests/test_widgets.py

@@ -3,7 +3,7 @@
 import operator
 from unittest import mock
 
-from matplotlib.backend_bases import MouseEvent
+from matplotlib.backend_bases import MouseEvent, DrawEvent
 import matplotlib.colors as mcolors
 import matplotlib.widgets as widgets
 import matplotlib.pyplot as plt
@@ -1757,3 +1757,26 @@ 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_radio, ax_checks) = plt.subplots(1, 2)
+
+    radio = widgets.RadioButtons(ax_radio, ['1', '2'], 0)
+    checks = widgets.CheckButtons(ax_checks, ['1', '2'], [True, False])
+
+    ax_checks.remove()
+    ax_radio.remove()
+    with io.BytesIO() as out:
+        # verify that saving does not raise
+        fig.savefig(out, format='raw')
+
+    # verify that this method which is triggered by a draw_event callback when
+    # blitting is enabled does not raise.  Calling private methods is simpler
+    # than trying to force blitting to be enabled with Agg or use a GUI
+    # framework.
+    renderer = fig._get_renderer()
+    evt = DrawEvent('draw_event', fig.canvas, renderer)
+    radio._clear(evt)
+    checks._clear(evt)

lib/matplotlib/widgets.py

@@ -117,7 +117,9 @@ def __init__(self, ax):
         self.ax = ax
         self._cids = []
 
-    canvas = property(lambda self: self.ax.get_figure(root=True).canvas)
+    canvas = property(
+        lambda self: getattr(self.ax.get_figure(root=True), 'canvas', None)
+    )
 
     def connect_event(self, event, callback):
         """
@@ -144,6 +146,10 @@ def _get_data_coords(self, event):
         return ((event.xdata, event.ydata) if event.inaxes is self.ax
                 else self.ax.transData.inverted().transform((event.x, event.y)))
 
+    def ignore(self, event):
+        # docstring inherited
+        return super().ignore(event) or self.canvas is None
+
 
 class Button(AxesWidget):
     """
@@ -2181,7 +2187,9 @@ def connect_default_events(self):
 
     def ignore(self, event):
         # docstring inherited
-        if not self.active or not self.ax.get_visible():
+        if super().ignore(event):
+            return True
+        if not self.ax.get_visible():
             return True
         # If canvas was locked
         if not self.canvas.widgetlock.available(self):