diff -r 358ccd42e052 -r 446b2c3da6e6 IDEFrame.py
--- a/IDEFrame.py	Tue Sep 07 09:08:40 2021 +0200
+++ b/IDEFrame.py	Thu Sep 09 09:37:03 2021 +0200
@@ -1409,7 +1409,8 @@
         self.AuiTabCtrl = auitabctrl
         if self.TabsOpened.GetPageCount() == 0:
             pane = self.AUIManager.GetPane(self.TabsOpened)
-            if pane.IsMaximized():
+            # on wxPython 4.1.0, AuiPaneInfo has no "IsMaximized" attribute...
+            if (not hasattr(pane, "IsMaximized")) or pane.IsMaximized():
                 self.AUIManager.RestorePane(pane)
             self.AUIManager.Update()
 
@@ -1497,7 +1498,8 @@
 
     def SwitchPerspective(self, evt):
         pane = self.AUIManager.GetPane(self.TabsOpened)
-        if pane.IsMaximized():
+        # on wxPython 4.1.0, AuiPaneInfo has no "IsMaximized" attribute...
+        if (not hasattr(pane, "IsMaximized")) or pane.IsMaximized():
             self.AUIManager.RestorePane(pane)
         else:
             self.AUIManager.MaximizePane(pane)