code: def shutdown(url=None):
      '''
      Stops the Host passed by parameter or all of them if none is
      specified, stopping at the same time all its actors.
      Should be called at the end of its usage, to finish correctly
      all the connections and threads.
      '''
      if url is None:
          for host in util.hosts.values():
              host.shutdown()
          global core_type
          core_type = None
      else:
          host = util.hosts[url]
          host.shutdown(f shutdown(url=None):
      '''
      Stops the Host passed by parameter or all of them if none is
      specified, stopping at the same time all its actors.
      Should be called at the end of its usage, to finish correctly
      all the connections and threads.
      '''
      if url is None:
          for host in util.hosts.values():
              host.shutdown()
          global core_type
          core_type = None
      else:
          host = util.hosts[url]
          host.shutdown()
docs: Stops the Host passed by parameter or all of them if none is
      specified, stopping at the same time all its actors.
      Should be called at the end of its usage, to finish correctly
      all the connections and threads.