First Class functions in Python

Last Updated : 01 Sep, 2025

In Python, functions are treated as first-class objects. This means they can be used just like numbers, strings, or any other variable. You can:

Assign functions to variables.
Pass them as arguments to other functions.
Return them from functions.
Store them in data structures such as lists or dictionaries.

This ability allows you to write reusable, modular and powerful code.

Characteristics of First-Class Functions

Functions in Python have the following important characteristics. Let’s see them one by one with examples:

1. Assigning Functions to Variables

We can assign a function to a variable and use the variable to call the function.

Example:

Python

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

# Assigning the function to a variable
f = msg

# Calling the function using the variable
print(f("Emma"))

Output

Hello, Emma!

Explanation:

The function msg is assigned to the variable f.
Now f can be used to call msg, showing that functions behave like variables.

2. Passing Functions as Arguments

Functions can be passed as arguments to other functions, enabling higher-order functions.

Example:

Python

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

def fun1(fun2, name):
    return fun2(name)

# Passing the msg function as an argument
print(fun1(msg, "Alex"))

Output

Hello, Alex!

Explanation:

The function fun1 takes another function (fun2) as input.
msg is passed to fun1, which then calls it with "Alex".

3. Returning Functions from Other Functions

A function can return another function, allowing for the creation of function factories.

Example:

Python

def fun1(msg):
    def fun2():
        return f"Message: {msg}"
    return fun2

# Getting the inner function
func = fun1("Hello, World!")
print(func())

Output

Message: Hello, World!

Explanation:

The function fun1 defines another function fun2 and returns it.
func stores the returned function fun2, which can be executed later.

4. Storing Functions in Data Structures

Functions can be stored in data structures like lists or dictionaries.

Example:

Python

def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

# Storing functions in a dictionary
d = {
    "add": add,
    "subtract": subtract
}

# Calling functions from the dictionary
print(d["add"](5, 3))       
print(d["subtract"](5, 3))

Output

8
2

Explanation:

Functions add and subtract are stored in a dictionary.
They are accessed using their keys and executed directly.

Suggested Quiz

8 Questions

Which of the following best describes a first-class function in programming languages?

A

A function that can only be called from within its own scope.
B

A function that can be assigned to variables, passed as arguments, and returned from other functions like any other object.
C

A function that can only be defined at the top level of a module.
D

A function that can only be executed in a specific context.

Explanation:

In the context of first-class functions, what is a higher-order function?

A

A function that can only return primitive data types.
B

A function that can take other functions as arguments or return them as results.
C

A function that is defined within another function but cannot be returned.
D

A function that executes in a separate thread.

Explanation:

What will be the output of the following code?

def greet(name):

return f"Hello, {name}"

say_hello = greet

print(say_hello("Geek"))

A

Hello, greet
B

greet
C

Hello, Geek
D

TypeError

Explanation:

Functions can be assigned to variables. Here, say_hello becomes another reference to greet.

Which of the following is not a property of first-class functions?

A

Functions can be stored in data structures
B

Functions can be assigned to variables
C

Functions can return other functions
D

Functions can only return primitive types

Explanation:

First-class functions can return any type, including other functions—not limited to primitives.

What will be the output of this code?

def outer():

def inner():

return "Inner function"

return inner

func = outer()

print(func())

A

Inner function
B

inner
C

outer
D

Error

Explanation:

outer() returns the inner function, and func() calls it, returning its string.

Which of the following is NOT a characteristic of first-class functions?

A

They can be assigned to variables.
B

They can be passed as arguments to other functions.
C

They can only be defined once in a program.
D

They can be returned from other functions.

Explanation:

What is the output of the following code?

def make_multiplier(n):

def multiplier(x):

return x * n

return multiplier

double = make_multiplier(2)

print(double(5))

A

7
B

10
C

25
D

Error

Explanation:

make_multiplier(2) returns a function that multiplies its argument by 2. So, double(5) returns 10.

How does Python treat functions with respect to variables?

A

Functions are static objects
B

Functions are constants and cannot be reassigned
C

Functions are first-class citizens and can be stored, passed, and reassigned
D

Functions must be declared global to be used

Explanation:

Being first-class citizens means functions can be assigned, passed, and returned like other objects.

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Article Tags :

Python

First Class functions in Python

Characteristics of First-Class Functions

1. Assigning Functions to Variables

2. Passing Functions as Arguments

3. Returning Functions from Other Functions

4. Storing Functions in Data Structures

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