<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_member(self, host_name, hostgroup_name):
 """Add a host string to a hostgroup member if the host group do not exist, create it :param host_name: host name :type host_name: str :param hostgroup_name:hostgroup name :type hostgroup_name: str :return: None """

        hostgroup = self.find_by_name(hostgroup_name)
        if not hostgroup:
            hostgroup = Hostgroup({'hostgroup_name': hostgroup_name,
                                   'alias': hostgroup_name,
                                   'members': host_name})
            self.add(hostgroup)
        else:
            hostgroup.add_members(host_name)