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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def rename_user(self, old_user, new_user):
 """Rename a JIRA user. :param old_user: Old username login :type old_user: str :param new_user: New username login :type new_user: str """

        if self._version > (6, 0, 0):
            url = self._options['server'] + '/rest/api/latest/user'
            payload = {
                "name": new_user}
            params = {
                'username': old_user}

            # raw displayName
            logging.debug("renaming %s" % self.user(old_user).emailAddress)

            r = self._session.put(url, params=params,
                                  data=json.dumps(payload))
            raise_on_error(r)
        else:
            raise NotImplementedError("Support for renaming users in Jira "
                                      "< 6.0.0 has been removed.")