Python Functions

Last Updated :04 Oct, 2025

Python Functions are a block of statements that does a specific task. The idea is to put some commonly or repeatedly done task together and make a function so that instead of writing the same code again and again for different inputs, we can do the function calls to reuse code contained in it over and over again.

Defining a Function

We can define a function in Python, using the def keyword. A function might take input in the form of parameters.

The syntax to declare a function is:

Here, we define a function using def that prints a welcome message when called.

Python

deffun():print("Welcome to GFG")

Calling a Function

After creating a function in Python we can call it by using the name of the functions followed by parenthesis containing parameters of that particular function.

Python

deffun():print("Welcome to GFG")fun()# Driver code to call a function

Output

Welcome to GFG

Function Arguments

Arguments are the values passed inside the parenthesis of the function. A function can have any number of arguments separated by a comma.

Syntax:

def function_name(parameters):
"""Docstring"""
# body of the function
return expression

We will create a simple function in Python to check whether the number passed as an argument to the function is even or odd.

Python

defevenOdd(x):if(x%2==0):return"Even"else:return"Odd"print(evenOdd(16))print(evenOdd(7))

Output

EvenOdd

Types of Function Arguments

Python supports various types of arguments that can be passed at the time of the function call. In Python, we have the following function argument types in Python, Let's explore them one by one.

1. Default Arguments

Adefault argument is a parameter that assumes a default value if a value is not provided in the function call for that argument.

Python

defmyFun(x,y=50):print("x: ",x)print("y: ",y)myFun(10)

Output

x:  10y:  50

2. Keyword Arguments

In keyword arguments, values are passed by explicitly specifying the parameter names, so the order doesn’t matter.

Python

defstudent(fname,lname):print(fname,lname)student(fname='Geeks',lname='Practice')student(lname='Practice',fname='Geeks')

Output

Geeks PracticeGeeks Practice

3. Positional Arguments

In positional arguments, values are assigned to parameters based on their order in the function call.

Python

defnameAge(name,age):print("Hi, I am",name)print("My age is ",age)print("Case-1:")nameAge("Suraj",27)print("\nCase-2:")nameAge(27,"Suraj")

Output

Case-1:Hi, I am SurajMy age is  27Case-2:Hi, I am 27My age is  Suraj

4. Arbitrary Arguments

In Python Arbitrary Keyword Arguments,*args and **kwargs can pass a variable number of arguments to a function using special symbols. There are two special symbols:

*args in Python (Non-Keyword Arguments)
**kwargs in Python (Keyword Arguments)

This code separately shows non-keyword (*args) and keyword (**kwargs) arguments in the same function.

Python

defmyFun(*args,**kwargs):print("Non-Keyword Arguments (*args):")forarginargs:print(arg)print("\nKeyword Arguments (**kwargs):")forkey,valueinkwargs.items():print(f"{key} =={value}")# Function call with both types of argumentsmyFun('Hey','Welcome',first='Geeks',mid='for',last='Geeks')

Output

Non-Keyword Arguments (*args):HeyWelcomeKeyword Arguments (**kwargs):first == Geeksmid == forlast == Geeks

Function within Functions

A function defined inside another function is called aninner function (or nested function). It can access variables from the enclosing function’s scope and is often used to keep logic protected and organized.

Python

deff1():s='I love GeeksforGeeks'deff2():print(s)f2()f1()

Output

I love GeeksforGeeks

Anonymous Functions

In Python, ananonymous function means that a function is without a name. As we already know the def keyword is used to define the normal functions and the lambda keyword is used to create anonymous functions.

Python

defcube(x):returnx*x*x# without lambdacube_l=lambdax:x*x*x# with lambdaprint(cube(7))print(cube_l(7))

Output

Return Statement in Function

Thereturnstatement ends a function and sends a value back to the caller. It can return any data type, multiple values (packed into a tuple), or None if no value is given.

Syntax:

return [expression]

Parameters: returnends the function, [expression]is the optional value to return (defaults to None).

Python

defsquare_value(num):"""This function returns the square    value of the entered number"""returnnum**2print(square_value(2))print(square_value(-4))

Output

Pass by Reference and Pass by Value

In Python, variables are references to objects. When we pass them to a function, the behavior depends on whether the object is mutable (like lists, dictionaries) or immutable (like integers, strings, tuples).

Mutable objects: Changes inside the function affect the original object.
Immutable objects: The original value remains unchanged.

Python

# Function modifies the first element of listdefmyFun(x):x[0]=20lst=[10,11,12,13]myFun(lst)print(lst)# list is modified# Function tries to modify an integerdefmyFun2(x):x=20a=10myFun2(a)print(a)# integer is not modified

Output

[20, 11, 12, 13]10

Note:Technically, Python uses "pass-by-object-reference". Mutable objects behave like pass by reference, while immutable objects behave like pass by value

Recursive Functions

Arecursive function is a function that calls itself to solve a problem. It is commonly used in mathematical and divide-and-conquer problems. Always include a base case to avoid infinite recursion.

Python

deffactorial(n):ifn==0:return1else:returnn*factorial(n-1)print(factorial(4))