<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_srv_by_name_and_hostname(self, host_name, sdescr):
 """Get a specific service based on a host_name and service_description :param host_name: host name linked to needed service :type host_name: str :param sdescr: service name we need :type sdescr: str :return: the service found or None :rtype: alignak.objects.service.Service """

        key = (host_name, sdescr)
        return self.name_to_item.get(key, None)