17.7: Operator overloading
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By defining other special methods, you can specify the behavior of operators on programmer-defined 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 + duration) 11:20:00
When you apply the + operator to Time objects, Python invokes
__add__. When you print the result, Python invokes
__str__. So there is a lot happening behind the scenes!
Changing the behavior of an operator so that it works with programmer-defined types is called operator overloading. For every operator in Python there is a corresponding special method, like
__add__. For more details, see http://docs.python.org/3/reference/datamodel.html#specialnames.
As an exercise, write an
add method for the Point class.