Decode GMaps Encoded Polyline

def __poly_decode_trans(value, index):
    """Transforms a GMaps Encoded polyline chunk back into numbers

    Args:
        value: chunk of the GMaps polyline
        index: position in the chunk

    Returns:
        chunk as a number
    """
    byte, result, shift = None, 0, 0

    while byte is None or byte >= 0x20:
        byte = ord(value[index]) - 63
        index += 1
        result |= (byte & 0x1F) << shift
        shift += 5
        comp = result & 1

    return ~(result >> 1) if comp else (result >> 1), index


def __poly_decode(expression, precision=5, geojson=False):
    """Transforms a GMaps Encoded polyline into a set of points

    Args:
        expression: the GMaps polyline
        precision: number of decimal places to calculate
        geojson: Return the sets in geojson compatible mode

    Returns:
        coordinates: list of points composing the polyline
    """
    coordinates, index, lat, lng, length, factor = (
        [],
        0,
        0,
        0,
        len(expression),
        float(10 ** precision),
    )

    while index < length:
        lat_change, index = __poly_decode_trans(expression, index)
        lng_change, index = __poly_decode_trans(expression, index)
        lat += lat_change
        lng += lng_change
        coordinates.append((lat / factor, lng / factor))

    if geojson is True:
        coordinates = [t[::-1] for t in coordinates]

    return coordinates