def dot_dir_dir(direction1, direction2):
    """ Evaluates the dot product of a direction with another direction.
    
    PARAMETERS
    ----------
    direction{1, 2}: Point
    
    RETURN
    ------
    : float
    """
    return sum((dir_coord1*dir_coord2 for dir_coord1, dir_coord2 in zip(direction1.coords, direction2.coords)))