Python Functions Tutorial for Beginners | AIML EP-5 | CHiPSET Tech Articles

Functions are one of the most important concepts in Python. They help you organize code into reusable blocks, making programs cleaner, shorter, and easier to manage.

What is a Function in Python?

A function is a block of code that performs a specific task. Instead of writing the same code multiple times, you can create a function once and use it whenever needed.

Image

image:wht is the use of function

image source:Geeksforgeeks

Example

Image

Here:

•def is used to define a function

•greet is the function name

•The code inside the function is called the function body

Why Use Functions?

Functions provide many advantages in programming.

Benefits of Functions

•Reduce code repetition

•Improve readability

•Make debugging easier

•Help organize large programs

•Allow code reusability

Image

image:syntax of the function

source: GeeksForGeeks

Creating a Function

In Python, functions are created using the def keyword.

Syntax

Image

Calling a Function

A function only runs when it is called.

Example

Image

Function with Parameters

Parameters allow functions to accept input values.

Image

Arguments are values passed to a function when it is called. They allow functions to receive input data and perform operations using those values.

Syntax

def function_name(arguments): # function body return value

•def function_name(arguments): defines a function with optional arguments.

•function body contains the statements to be executed.

•return value returns a result from the function. If no return statement is used, it returns None by default.

Function with Multiple Parameters

You can pass multiple values into a function.

Example

def add(a, b):

print(a + b)

add(5, 3)

Output

Return Statement in Functions

The return keyword sends a value back from the function.

Image

Difference Between print() and return

Using print()

def add(a, b):

print(a + b)

•Displays output directly

•Cannot store the value easily

Using return

def add(a, b):

return a + b

•Sends value back

•Can store and reuse the result

Types of Functions in Python

Built-in Functions

Python already provides many ready-made functions.

Examples

print()

len()

type()

input()

User-defined Functions

Functions created by programmers are called user-defined functions.

Example

def multiply(a, b):

return a * b

1. Default argument: Default argument use a predefined value when no value is passed during the function call.

Image

Keyword Arguments

pass values using parameter names, so argument order does not matter.

example shown below

Image

Local Variables

•A local variableis a variable that is declared inside a function.

•It only exists while the function is running.

•Once the function finishes, the variable is destroyed and cannot be accessed outside.

Image

Here:

•x is created inside the function test().

•When you call test(), Python prints 10.

•But if you try print(x) outside the function, you’ll get an error because x only lives inside test().

Global Variables

•A global variable is declared outside of all functions.

•It can be accessed by any function in the program (unless shadowed by a local variable with the same name).

•It exists as long as the program runs.

Example:

Image

Here:

•x is defined outside the function, so it’s global.

•The function show() can directly access it and prints 20.

•Even if you call print(x) outside the function, it will still print 20.

Positional Arguments: values are assigned to parameters based on their order in the function call.

example:

Image

Function within Functions

A function defined inside another function is called an inner function (or nested function). It is used to organize related logic and access variables from the outer function.

Image

Pass by Reference and Pass by Value

🔹 First, the big picture

•In Python, everything is an object (numbers, strings, lists, etc.).

•When you pass a variable into a function, Python doesn’t copy the object itself. Instead, it passes a reference to the object.

•Whether the function can change the original object depends on whether the object is mutable or immutable.

🔹 Mutable vs Immutable

•Mutable objects: Can be changed in place. Examples → list, dict, set.

•Immutable objects: Cannot be changed in place. Examples → int, float, str, tuple.

Key Concept: "Pass-by-object-reference"

•Python doesn’t use pass-by-value (like C, where a copy is made).

•Python doesn’t use pass-by-reference (like C++ with pointers, where you can directly change the caller’s variable).

•Instead, Python uses pass-by-object-reference:

•The function receives a reference to the object.

•If the object is mutable, changes inside the function affect the original.

•If the object is immutable, reassignment inside the function only affects the local reference.

🧠 Analogy

Think of variables as name tags pointing to boxes:

•If the box is a mutable container (like a list), you can open it and change what’s inside → everyone sees the change.

•If the box is an immutable sealed box (like an integer), you can’t change what’s inside. You can only stick your name tag on a different box → but that doesn’t move other people’s name tags.

Python Lambda Functions

Image

🔹 What is a Lambda Function?

A lambda functionis just a small, anonymous function— meaning it has no name.It’s used when you need a quick, one-line function for short tasks.

Think of it like a shortcut: instead of writing a full defblock, you write a one-liner.

Syntax

python

lambda arguments: expression

•lambda → keyword that defines the function

•arguments → input values (like parameters)

•expression → what the function returns (automatically)

Image

Multiple arguments

Image

Recursive Functions

A recursive function calls itself repeatedly until a condition is met.

Example

Image

Common Errors in Functions

Forgetting Parentheses

greet

Correct:

greet()

Missing Return Statement

def add(a, b): a + b

Correct:

def add(a, b): return a + b

Conclusion

Python functions help make programs modular, reusable, and easier to understand. By learning how to create, call, and use functions effectively, you can write cleaner and more professional Python code.

previous episode: Python Loops Explained | For Loop and While Loop | AIML EP-4 | CHiPSET Tech Articles | CHIPSET SRM University Ramapuram