code: def list_users(self, pattern=None):
          
          request_url = "{}/api/0/users".format(self.instance)
          params = None
          if pattern:
              params = {'pattern': pattern}
          return_value = self._call_api(request_url, params=params)
          return return_value['users']
docs: List all users registered on this Pagure instance.
          :param pattern: filters the starting letters of the return value
          :return: