Merge pull request #13121 from meeseeksmachine/auto-backport-of-pr-13091-on-7.x

Backport PR  #13091 on branch 7.x (Fix for issue  #12897)

IPython/terminal/interactiveshell.py

@@ -168,9 +168,8 b' class TerminalInteractiveShell(InteractiveShell):'
 
     @observe('editing_mode')
     def _editing_mode(self, change):
-        u_mode = change.new.upper()
         if self.pt_app:
-            self.pt_app.editing_mode = u_mode
+            self.pt_app.editing_mode = getattr(EditingMode, change.new.upper())
 
     @observe('autoformatter')
     def _autoformatter_changed(self, change):