@staticmethod<EOL><INDENT>def get_sender(doc):<DEDENT>
key_id = doc.find("<STR_LIT>" % NAMESPACE).get("<STR_LIT>")<EOL>return urlsafe_b64decode(key_id).decode("<STR_LIT:utf-8>")<EOL>
Get the key_id from the `sig` element which contains urlsafe_b64encoded Diaspora handle.

        :param doc: ElementTree document
        :returns: Diaspora handle