class LineSegment:
    '''A line segment from one Point to another Point.'''
    
    def __init__(self, start_point, end_point):
        '''Initializes the line segment by storing the start and endpoints.'''
        self.start_point = start_point
        self.end_point = end_point
    
    
    def slope(self):
        '''Return the slope of the line segment.'''
        change_y = self.end_point.y - self.start_point.y
        change_x = self.end_point.x - self.start_point.x
        return change_y / change_x
    
    
    def length(self):
        '''Return the length of the line segment.'''
        return self.start_point.distance_to(self.end_point)


    def __str__(self):
        '''Return a string version of the line segment.'''
        return 'Line from ' + str(self.start_point) + ' to ' + str(self.end_point)


def main():
    '''Test the LineSegment class.'''
    p1 = Point(3, 7)
    p2 = Point(-10, 1)
    line = LineSegment(p1, p2)
    print("line is " + str(line))
    linelen = line.length()
    print("length of line is " + str(linelen))
    lineslope = line.slope()
    print("slope of line is " + str(lineslope))
        
main()