@staticmethod
def get_quadkeys(col: int, row: int, zoom: int) ->str:
    """This function is used to encode (col, row, zoom) as quadkey. For details, refer to
        https://developer.here.com/rest-apis/documentation/traffic/common/map_tile/topics/quadkeys.html

        Args:
            col (int): column
            row (int): row
            zoom (int): the zoom level

        Returns:
            str: quadkey

        Example:
            >>> # or checkout the unittest for this function
            >>> settings = {
                    'app_id': 'F8aPRXcW3MmyUvQ8Z3J9',
                    'app_code' : 'IVp1_zoGHdLdz0GvD_Eqsw',
                    'map_tile_base_url': 'https://1.traffic.maps.cit.api.here.com/maptile/2.1/traffictile/newest/normal.day/',
                    'json_tile_base_url': 'https://traffic.cit.api.here.com/traffic/6.2/flow.json?'
                }
            >>> util = Utility(settings)
            >>> util.get_quadkeys(35210, 21493, 16)
            "1202102332221212"
        """
    quadkey = ''
    for i in range(zoom, 0, -1):
        digit = 0
        mask = 1 << i - 1
        if col & mask != 0:
            digit += 1
        if row & mask != 0:
            digit += 2
        quadkey += str(digit)
    return quadkey
