How to overload `float()` for a custom class in Python?

Question

Summary

How can I overload the built-in float for my class so when I call float() on an instance of it, my custom function gets called in

Answer 1

Define the __float__() special method on your class.

class MyClass(object):
    def __float__(self):
         return 0.0

float(MyClass())   # 0.0

Note that this method must return a float! The calculation self.num / self.denom, returns an int by default in versions of Python prior to 3.0 assuming both operands are integers. In this case you'd just make sure one of the operands is a float: float(self.num) / self.denom for example.