Ensure the notebook still exists as the delivery of the changed and changing events may not happen right away

demo/Notebook.py

@@ -85,6 +85,7 @@ class TestNB(wx.Notebook):
 
 
     def OnPageChanged(self, event):
+        if self:
             old = event.GetOldSelection()
             new = event.GetSelection()
             sel = self.GetSelection()
@@ -92,6 +93,7 @@ class TestNB(wx.Notebook):
         event.Skip()
 
     def OnPageChanging(self, event):
+        if self:
             old = event.GetOldSelection()
             new = event.GetSelection()
             sel = self.GetSelection()