code: def get_agents(self, addr=True, agent_cls=None, include_manager=False):
          '''Get agents in the environment.
          :param bool addr: If ``True``, returns only addresses of the agents.
          :param agent_cls:
              Optional, if specified returns only agents belonging to that
              particular class.
          :param bool include_manager:
              If `True``` includes the environment's manager, i.e. the agent in
              the address ``tcp://environment-host:port/0``, to the returned
              list if the environment has attribute :attr:`manager`. If
              environment does not have :attr:`manager`, then the parameter does
              nothing.
          :returns: A list of agents in the environment.
          :rtype: list
          .. note::
              By design, manager agents are excluded from the returned lists of
              agents by default.
          '''
          agents = list(self.agents.dict.values())
          if hasattr(self, 'manager') and self.manager is not None:
              if not include_manager:
                  agents = [a for a in agents if a.addr.rsplit('/', 1)[1] != '0']
          if agent_cls is not None:
              agents = [a for a in agents if type(a) is agent_cls]
          if addr:
              agents = [agent.addr for agent in agents]
          return agents