def _distance_2p(x1, y1, x2, y2):
    """
    calculates the distance between two given points
    :param x1: starting x value
    :param y1: starting y value
    :param x2: ending x value
    :param y2: ending y value
    :return: the distance between [x1, y1] -> [x2, y2]
    """
    return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5