Return the slope m of this line segment.

def get_slope(self):
        """Return the slope m of this line segment."""
        # y1 = m*x1 + t
        # y2 = m*x2 + t => y1-y2 = m*(x1-x2) <=> m = (y1-y2)/(x1-x2)
        return ((self.p1.y-self.p2.y) / (self.p1.x-self.p2.x))