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Operator overloading

8 September, 2015 - 10:43

By defining other special methods, you can specify the behavior of operators on userdefined types. For example, if you define a method named __add__ for the Time class, you can use the + operator on Time objects.

Here is what the definition might look like:

# inside class Time:
def __add__(self, other):
seconds = self.time_to_int() + other.time_to_int()
return int_to_time(seconds)

And here is how you could use it:

>>> start = Time(9, 45)>>> duration = Time(1, 35)>>> print start + duration11:20:00

When you apply the + operator to Time objects, Python invokes __add__. When you print the result, Python invokes __str__. So there is quite a lot happening behind the scenes!

Changing the behavior of an operator so that it works with user-defined types is called operator overloading. For every operator in Python there is a corresponding special method, like __add__. For more details, see

Exercise 17.4.Write an add method for the Point class.