Python: how to define a class that behaves like a function? [duplicate]

Question

I would like to define in python a class that behaves like a function with additional attributes. In particular, it should be seamlessly applied to a variable.

Let’s try to explain with a mathematical example. Say I am very much into sinusoïdal functions, but also interested by their frequency. A function x -> sin(omega x) has the attribute frequency, namely the value of omega. It can also be applied to a float x.

I can write:

from numpy import sin, pi

class SinFunc:
    def __init__(self, omega):
        self.frequency = omega

    def apply_to(self, x):
        return sin(self.frequency * x)

I could then play with a sinusoïdal function:

MySinFunc = SinFunc(3)
print(MySinFunc.frequency)
print(MySinFunc.apply_to(pi)) 
# output
# 3
# 0 (almost!)

But what I would like is to be able to write directly MySinFunc(pi), with the attribute frequency still defined.

How to achieve that? Thanks!

Answer 1

To make an object callable, you need to add a __call__ class method that will handle the call.

Rename your apply_to function to __call__ and it will work.