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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 __get_query_range(cls, date_field, start=None, end=None):
 """ 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. """

        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