def _roster_set(self, item, callback, error_callback):
stanza = Iq(to_jid = self.server, stanza_type = "<STR_LIT>")<EOL>payload = RosterPayload([item])<EOL>stanza.set_payload(payload)<EOL>def success_cb(result_stanza):<EOL><INDENT>"""<STR_LIT>"""<EOL>if callback:<EOL><INDENT>callback(item)<EOL><DEDENT><DEDENT>def error_cb(error_stanza):<EOL><INDENT>"""<STR_LIT>"""<EOL>if error_callback:<EOL><INDENT>error_callback(error_stanza)<EOL><DEDENT>else:<EOL><INDENT>logger.error("<STR_LIT>".format(item.jid))<EOL><DEDENT><DEDENT>processor = self.stanza_processor<EOL>processor.set_response_handlers(stanza,<EOL>success_cb, error_cb)<EOL>processor.send(stanza)<EOL>
Send a 'roster set' to the server.

        :Parameters:
            - `item`: the requested change
        :Types:
            - `item`: `RosterItem`