6. Functions in Python

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6. Functions in Python

May 24, 2026 in Python

Functions are reusable blocks of code used to perform specific tasks.

Functions help:

  • Reduce code repetition
  • Improve readability
  • Make programs modular

Defining Functions

Use the def keyword to create a function.

Syntax

def function_name():
    # code

Example

def greet():
    print("Hello, Welcome to Python")

Calling the function:

greet()

Output:

Hello, Welcome to Python

Function with Parameters

Parameters allow passing data to functions.

def greet(name):
    print("Hello", name)

greet("Aditya")

Output:

Hello Aditya

Function Arguments

Arguments are values passed to functions.

Python supports different types of arguments.

1. Positional Arguments

Arguments are assigned based on position.

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

add(10, 20)

Output:

30

2. Keyword Arguments

Arguments are assigned using parameter names.

def student(name, age):
    print(name, age)

student(age=25, name="Aditya")

3. Default Arguments

Default values are used if argument is not provided.

def greet(name="Guest"):
    print("Hello", name)

greet()
greet("Rahul")

Output:

Hello Guest
Hello Rahul

4. Variable-Length Arguments

Used when number of arguments is unknown.

*args

Accepts multiple positional arguments.

def total(*numbers):
    print(numbers)

total(1, 2, 3, 4)

Output:

(1, 2, 3, 4)

Sum Using *args

def add(*numbers):
    total = 0

    for num in numbers:
        total += num

    print(total)

add(1, 2, 3)

**kwargs

Accepts multiple keyword arguments.

def details(**data):
    print(data)

details(name="Aditya", age=25)

Output:

{'name': 'Aditya', 'age': 25}

Return Statement

The return statement sends value back from function.

Example

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

result = add(10, 20)

print(result)

Output:

30

Multiple Return Values

def calculation(a, b):
    return a + b, a - b

sum_value, sub_value = calculation(10, 5)

print(sum_value)
print(sub_value)

Lambda Functions

Lambda functions are anonymous small functions.

Syntax

lambda arguments : expression

Example

square = lambda x: x * x

print(square(5))

Output:

25

Lambda with Multiple Arguments

add = lambda a, b: a + b

print(add(10, 20))

Recursive Functions

A recursive function calls itself.

Used for problems that can be broken into smaller similar problems.

Example: Factorial

def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n - 1)

print(factorial(5))

Output:

120

Example: Fibonacci Series

def fibonacci(n):
    if n <= 1:
        return n
    return fibonacci(n - 1) + fibonacci(n - 2)

for i in range(6):
    print(fibonacci(i))

Output:

0
1
1
2
3
5

Scope and Lifetime of Variables

Scope defines where a variable can be accessed.

1. Local Variables

Declared inside function.

Accessible only inside that function.

def test():
    x = 10
    print(x)

test()

Example: Error Outside Function

def demo():
    y = 20

demo()

# print(y)  # Error

2. Global Variables

Declared outside function.

Accessible everywhere.

name = "Python"

def show():
    print(name)

show()
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Modifying Global Variable

Use global keyword.

count = 0

def increase():
    global count
    count += 1

increase()

print(count)

Output:

1

Lifetime of Variables

  • Local variables exist only during function execution.
  • Global variables exist throughout program execution.

Nested Functions

Function inside another function.

def outer():
    
    def inner():
        print("Inside Inner Function")
    
    inner()

outer()

Practical Example

Calculator Function

def calculator(a, b):

    print("Addition:", a + b)
    print("Subtraction:", a - b)
    print("Multiplication:", a * b)
    print("Division:", a / b)

calculator(10, 5)

aditya singh