Classes are callable

What is the output of running the code below?

print(int("3"))  # ??

If you guessed “3”, then you are obviously correct. The built-in int turns strings into integers, when such a conversion is reasonable, and you can read about its behaviour in the documentation page called “Built-in functions”. However, the built-in int is not, strictly speaking, a function…

The built-in print is a function:

print(type(print))  # <class 'builtin_function_or_method'>

However, the built-in int produces a different output:

print(type(int))  # <class 'type'>

The output says that int is a type, which means that int is a class! It’s a built-in class, but a class. All this to say that classes can also be called with parenthesis () after their name…

And the decorator syntax with the at sign @ doesn’t really require a function… Since the at sign syntax @decorator around a function fn translates into the call decorator(fn), classes can also be used as decorators! But is that useful?