Suppose you have created a Vector class to represent two-dimensional vectors, what happens when you use the plus operator to add them? Most likely Python will yell at you.
You could, however, define the __add__ method in your class to perform vector addition and then the plus operator would behave as per expectation −
#!/usr/bin/python class Vector: def __init__(self, a, b): self.a = a self.b = b def __str__(self): return 'Vector (%d, %d)' % (self.a, self.b) def __add__(self,other): return Vector(self.a + other.a, self.b + other.b) v1 = Vector(2,10) v2 = Vector(5,-2) print v1 + v2
When the above code is executed, it produces the following result −