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Returning a function from a function - Python

Last Updated : 19 Mar, 2025

In Python, functions are first-class objects, allowing them to be assigned to variables, passed as arguments and returned from other functions. This enables higher-order functions, closures and dynamic behavior.

Example:

def fun1(name):
    def fun2():
        return f"Hello, {name}!"
    return fun2

# Get the function returned by fun1()
msg = fun1("shakshi")

# Call the returned function
print(msg()) 

Explanation: fun1 defines fun2, which captures the name parameter. When called with "shakshi", fun1 returns fun2, assigned to msg. Calling msg() returns "Hello, shakshi!".

It's essential to understand what makes functions "first-class" in Python. A first-class object is an entity that can be:

• Assigned to a variable: Functions can be stored in variables, just like other data types (e.g., integers, strings).
• Passed as arguments: Functions can be passed as arguments to other functions.
• Returned from other functions: Functions can be returned from other functions.
• Stored in data structures: Functions can be stored in lists, dictionaries, or other data structures.

Because functions are first-class objects, they provide flexibility in designing highly reusable and dynamic programs

Example 1: Returning a Function Without Arguments

def B():
    print("Inside the method B.")

def A():
    print("Inside the method A.") 
    return B  # function A returns function B

return_fun = A()  # call A(), which returns function B
return_fun()  # call function B through return_fun

Inside the method A.
Inside the method B.

Explanation: When A() is called, it returns B, which is assigned to return_fun. Calling return_fun() invokes B .

Example 2: Returning a function with arguments

def B(st2):
    print("Good " + st2 + ".")

def A(st1, st2):
    print(st1 + " and ", end="")  
    B(st2)  # call B with st2

A("Hello", "Morning")  # call A with two arguments

Hello and Good Morning.

Explanation: A calls B with st2 as an argument. When A("Hello", "Morning") is called, it prints "Hello and " and then calls B("Morning")

Example 3: Returning a lambda function

def A(u, v):
    w = u + v  # Sum of u and v
    z = u - v  # Difference of u and v
    
    return lambda: print(w * z)  # return lambda to print product of w and z

return_fun = A(5, 2)  # get lambda function
print(return_fun)

return_fun()  # execute lambda

<function A.<locals>.<lambda> at 0x7faef1653380>
21

Explanation: A calculates the sum (w) and difference (z) of u and v, then returns a lambda function that prints the product of w and z. When A(5, 2) is called, it returns the lambda, which is assigned to return_fun.

Returning functions from functions is a versatile and powerful feature in Python. It can be used in various scenarios, such as:

• Callbacks: Functions can be returned to be called later in response to some event.
• Closures: Functions can capture variables from the enclosing scope, enabling encapsulation and maintaining state across function calls.
• Function Generators: Functions can be returned based on parameters, allowing dynamic creation of behavior at runtime.
• Decorators: Decorators are a form of higher-order functions that modify or enhance other functions by returning a new function.

Example: Creating a custom power function

def power(exponent):
    return lambda base: base ** exponent  # return lambda to raise base to exponent

square = power(2)  # function to square a number
cube = power(3)    # function to cube a number

print(square(5))  # square 5
print(cube(3))    # cube 3

Explanation: power() returns a lambda function that raises a number (base) to a given exponent. Calling power(2) creates a function square to square a number and calling power(3) creates a function cube to cube a number.

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