__call__ in Python

Hello there! In this story, we will discuss how to use __call__ in Python classes. With __call__, you can use class objects as functions, which means you first initialize the object and then use it as a function. Essentially, it makes your object callable (all methods in Python are callable objects!).

Let’s take a look at an example:

class MyClass:
    def __call__(self):
        print('hi')


my_object = MyClass()
my_object()

It will print hi in the console. Let’s take a look at a more complex example.

import secrets

class TokenUrlsafeGenerator:
    length: int

    def __init__(self, length: int):
        self.length = length

    def __call__(self) -> str:
        return secrets.token_urlsafe(self.length)


token_generator = TokenUrlsafeGenerator(length=32)
token = token_generator()

Let’s break this example down to understand how the code works:

First of all, you can use the secrets module in Python. You can refer to the Python documentation for more details, but in short, this module will help you generate secure and random numbers or strings to manage the secrets of your project.

You can see the TokenUrlsafeGenerator class, which is initialized with a length argument. The __call__ method is used to generate the token based on this length. To generate secure tokens, we simply need to create an instance of this class and call it. It's as simple as that!

You can pass arguments to __call__ just like the other functions in Python. See the following example:

class Adder:

    def __call__(self, arg1, arg2):
        return arg1 + arg2


adder = Adder()
result = adder(1, 2)

In this example, the variable result will have a value of 3.

Conclusion

In this story, we learned how to convert a Python object into a callable one by using the __call__ method. This method provides us with the full functionality of functions in Python.

Hope you enjoy!