class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Point({0}, {1})".format(self.x, self.y)
    def __add__(self, other):
        a = self.x + other.x
        b = self.y + other.y
        return "Point({a}, {b})"
    def __sub__(a, b):
        c = self.x - other.x
        d = self.y - other.y
        return "Point({c}, {d})"

class Point(object):
    __slots__ = ['x', 'y']
    
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Point({0}, {1})".format(self.x, self.y)
    def __add__(self, other):
        x, y = self.x + other.x, self.y + other.y
        return self.__class__(x, y)
    def __sub__(self, other):
        x, y = self.x - other.x, self.y - other.y
        return self.__class__(x, y)

1. added __slots__ to save memory of the crated object from class
   
2. method signature of sub was wrong
   
3. A Point should be immutable. Doing an operation with two points, should return a new point.
   
   Instead of self.__class__, you can use also direct the name Point.
   The first one is good for inheritance.