<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_host(self, hostname):
 """ Get an existing host or otherwise initialize a new empty one. """

        if hostname not in self.hosts:
            self.hosts[hostname] = {
                'groups': set(),
                'hostvars': {}
            }
        return self.hosts[hostname]