__call__ in Python

Python has a set of built-in methods and __call__ is one of them. The __call__ method enables Python programmers to write classes where the instances behave like functions and can be called like a function. When this method is defined, calling an object (obj(arg1, arg2)) automatically triggers obj.__call__(arg1, arg2). This makes objects behave like functions, enabling more flexible and reusable code.

Syntax:

class Example:
def __init__(self):
# code

# Defining __call__ method
def __call__(self):
# code

• def __call__(self): defines a method that can be called as a function directly from the instance of the class Example.

Examples of __call__

Let's understand the implementation of __call__ in Python with the help of some code examples.

Example 1: Basic Usage

In this example, we will define a class and create a __call__ method in it and call it using the object of the that:

class Gfg:
    def __init__(self):
        print("Instance Created")
    
    # Defining __call__ method
    def __call__(self):
        print("Instance is called via special method")

# Instance created
e = Gfg()

# __call__ method will be called
e()

Instance Created
Instance is called via special method

Explanation:

• __init__ method runs when the object is created.
• __call__ method is triggered when we use e() like a function.
• This makes Gfg instances callable.

Example 2: Passing Arguments

Now let's see how to pass arguments to such methods:

class Prod:
    def __init__(self):
        print("Instance Created")

    # Defining __call__ method
    def __call__(self, a, b):
        print(a * b)

# Instance created
a = Prod()

# __call__ method will be called
a(10, 20)

Instance Created
200

Explanation:

• __call__ accepts arguments (a, b), allowing instances to process input like a function.
• This is useful for creating flexible objects that act as parameterized functions.

Example 3: Creating a Counter Function

Lets's create a counter object using __call__:

class C:
    def __init__(self):
        self.count = 0

    def __call__(self):
        self.count += 1
        return self.count

count = C()
print(count()) 
print(count())  
print(count()) 

1
2
3

Exlpanation:

• Counter object keeps track of how many times it has been called.
• This is useful for rate limiting, caching, or tracking API calls.