code: def _to_df(self, query, conn, index_col=None, coerce_float=True, params=None,
                 parse_dates=None, columns=None):
          
          return pd.io.sql.read_sql(str(query), conn, index_col=index_col,
                                    coerce_float=coerce_float, params=params,
                                    parse_dates=parse_dates, columns=columns)
docs: Internal convert-to-DataFrame convenience wrapper.