code: def do_undisplay(self, arg):
          
          if arg:
              try:
                  del self.displaying.get(self.curframe, {})[arg]
              except KeyError:
                  self.error('not displaying %s' % arg)
          else:
              self.displaying.pop(self.curframe, None)
docs: undisplay [expression]
  
          Do not display the expression any more in the current frame.
  
          Without expression, clear all display expressions for the current frame.