code: def __get_query_range(cls, date_field, start=None, end=None):
          
          if not start and not end:
              return ''
  
          start_end = {}
          if start:
              start_end["gte"] = "%s" % start.isoformat()
          if end:
              start_end["lte"] = "%s" % end.isoformat()
  
          query_range = {date_field: start_end}
          return query_range
docs: Create a filter dict with date_field from start to end dates.
  
          :param date_field: field with the date value
          :param start: date with the from value. Should be a datetime.datetime object
                        of the form: datetime.datetime(2018, 5, 25, 15, 17, 39)
          :param end: date with the to value. Should be a datetime.datetime object
                        of the form: datetime.datetime(2018, 5, 25, 15, 17, 39)
          :return: a dict containing a range filter which can be used later in an
                   es_dsl Search object using the `filter` method.