gistfile1.py

class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __sub__(self, other):
        """Distance between two points
        
        Point(1, 1) - Point(1, 0) == 1
        """
        
        if not isinstance(other, Point):
            raise NotImplementedError("Must subtract Points from Points")
        return ((self.x - other.x) ** 2 + (self.y - other.y) ** 2) ** 0.5

# Magically growing bicycle!!

center_of_mass = Point(0, 0)  # flat area
rear_tire = Point(-2, 0)
front_tire = Point(2, 0)
bike_length = front_tire - rear_tire  # 4.0

center_of_mass = Point(10, 0)  # very bumpy right here!
rear_tire = Point(8, -4)   # -2 pixels twice
front_tire = Point(12, 4)  # +2 pixels twice
bike_length = front_tire - rear_tire  # 8.94427190999916  OVER TWICE THE LENGTH!