code: def do_display(self, arg):
          
          if not arg:
              self.message('Currently displaying:')
              for item in self.displaying.get(self.curframe, {}).items():
                  self.message('%s: %s' % bdb.safe_repr(item))
          else:
              val = self._getval_except(arg)
              self.displaying.setdefault(self.curframe, {})[arg] = val
              self.message('display %s: %s' % (arg, bdb.safe_repr(val)))
docs: display [expression]
  
          Display the value of the expression if it changed, each time execution
          stops in the current frame.
  
          Without expression, list all display expressions for the current frame.