code: def do(self, command):
          
          echo = self.echo and command or ''
          if not self.logged_in:
              return echo + '\n' + self._get_prompt()
  
          response = self.commands.eval(command)
          if response is None:
              return echo + '\n' + self._get_prompt()
          return echo + response
docs: "Executes" the given command on the virtual device, and returns
          the response.
  
          :type  command: str
          :param command: The command to be executed.
          :rtype:  str
          :return: The response of the virtual device.