def exportValue(self, vf, value):
        m = StrStrHashMap(value)
        keysAndValues = []
        for i in m.keys():
            keysAndValues.append(i)
            keysAndValues.append(m[i])
def test_impl():
            df = pq.read_table('example.parquet').to_pandas()
            return df.four.nunique()