code: def get_straight_line_transfer_distances(self, stop_I=None):
          
          if stop_I is not None:
              query = u""" SELECT from_stop_I, to_stop_I, d
                          FROM stop_distances
                              WHERE
                                  from_stop_I=?
                      """
              params = (u"{stop_I}".format(stop_I=stop_I),)
          else:
              query = """ SELECT from_stop_I, to_stop_I, d
                          FROM stop_distances
                      """
              params = None
          stop_data_df = pd.read_sql_query(query, self.conn, params=params)
          return stop_data_df
docs: Get (straight line) distances to stations that can be transferred to.
  
          Parameters
          ----------
          stop_I : int, optional
              If not specified return all possible transfer distances
  
          Returns
          -------
          distances: pandas.DataFrame
              each row has the following items
                  from_stop_I: int
                  to_stop_I: int
                  d: float or int #distance in meters