docs: def set_connection(self, service_name, to_cache):
          """
          Sets a connection class within the cache.
  
          :param service_name: The service a given ``Connection`` talks to. Ex.
              ``sqs``, ``sns``, ``dynamodb``, etc.
          :type service_name: string
  
          :param to_cache: The class to be cached for the service.
          :type to_cache: class
          """
          self.services.setdefault(service_name, {})
          self.services[service_name]['connection'] = to_cache