Python __call__() Magic Method

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Syntax

object.__call__(self[, args...])

The Python __call__ method makes a class callable, so you can call objects of the class like a normal function. For example, if you define __call__(self) on an object x of class X, you can call it like so: x(). The return value of the called object is the return value of the __call__() method.

We call this a “Dunder Method” for Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.

💡 Note: Formally, calling x(arg1, arg2, ...) translates to type(x).__call__(x, arg1, ...) whereas the type() built-in function determines the class (type) of x.

Minimal Example __call__

The following code snippet makes a custom class Person callable by providing an implementation of the magic method __call__() that takes two arguments:

  • self – a reference to the object itself. This is automatically passed into the function by Python—you don’t need to provide the argument yourself.
  • other – an additional argument (e.g., a string) to provide a custom greeting.

With this implementation, we can now create a callable object alice and call it like so: alice().

class Person:
    def __call__(self, other):
        return f'Hi {other}'


alice = Person()
print(alice('Bob'))
# Hi Bob

Background callable

Python callable() | Wow!!! 🐍🐍 What a Great Python Trick!

Python’s built-in callable(object) returns True if you could call the object argument like a function with the trailing parentheses in object().

You can make any object callable by implementing the instance’s __call__() method.

For example, callable(callable) returns True because callable is a function object. But callable(3) returns False because an integer is not a function you can call.

>>> callable(callable)
True
>>> callable(3)
False

You can learn more about the function in our detailed blog guide:

References:

Where to Go From Here?

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