What is a Function in Python?

What is a Function in Python?

A function is a reusable block of code that runs only when you call it.

Basic Syntax

# DEFINING a function
def function_name(parameters):
# code block
return result
# CALLING a function
function_name(arguments)

Simplest Example

# Define once

def say_hello():
print("Hello, World!")

# Call anytime, anywhere
say_hello() # Hello, World!
say_hello() # Hello, World!
say_hello() # Hello, World!

Functions with Parameters (Inputs)

# One parameter

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

greet("Alice") # Hello Alice
greet("Bob") # Hello Bob

# Two parameters

def add(a, b):
print(a + b)
add(3, 5) # 8
add(10, 20) # 30

4 Types of Functions:

1️ No Input, No Output
2 Input, No Output
3 No Input, With Output
4 Input AND Output

1️ No Input, No Output

def say_hello():
print("Hello!")
say_hello()

2 Input, No Output

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

3 No Input, With Output

def get_pi():
return 3.14159
pi = get_pi()
print(pi) # 3.14159

4 Input AND Output

def multiply(a, b):
return a * b
result = multiply(4, 5)
print(result) # 20

# Why we use functions?

To avoid repeating the same code again and again.

# Creating and calling a function

def text():
print("Hello Welcome to python Functions")
text()
text()

a = 3
b = 5
multiplication = a*b
print(multiplication)

a = 11
b = 15
multiplication = a*b
print(multiplication)

a = 20
b = 35

multiplication = a*b
print(multiplication)'''

# funtion with parameters

def multiplication(a, b):
print(a * b)
multiplication(6, 7)
multiplication(55, 60)'''

def addition(q, r):
print(q + r)
addition(20, 35)
addition(3500, 3223)
addition(25,45)'

def greet_user(name):

print(f"Hello {name} Glad To Meet You!")
greet_user("Qader")
greet_user("Lubna")
greet_user("Shoaib")
greet_user("Rumaysa")'''

#creating and calling a function (without parameters)

def text():
print("Hello Qader Welcome To Python Funtions!")
text()

#creating and calling a function (with parameters)

def multiplication(a,b):
print(a * b)
multiplication(5, 9) # multiplication

#creating and calling a function (with parameters)

def addition(a,b):
print(a + b)
addition(15, 15) #addition

#creating and calling a function (with parameters)

def division(a,b):
print(a / b)
division(20, 5) #division

#creating and calling a function (with parameters)

def substraction(a,b):
print(a - b)
substraction(35, 30) # substraction

def greet_user(name):
print(f"Hello{name} Glad to Meet You!")
greet_user("Mohammed Qadar")
greet_user("MohammedQadar")
greet_user("MQadar")
greet_user("QadarM")

-Return statement in Functions:

def add(a,b):
return a + b
result=add(5,5)
print("sum ", result)

-Default parameters in function?

Syntax:

def welcome(name= "Guest"):
print(f"welcome, {name}!")
welcome()
welcome("Qader")

Example:

def welcome(name= "khadar"):
print(f"welcome {name} great to see you!")
welcome()
welcome("qader")

# Billing system example:

def calculate_total(price, tax=0.05):
total= price + (price * tax)
return total
print(calculate_total(100))
print(calculate_total(100, 0.08))

# Keywords and Arguments in Functions?

Syntax:

def student_info(name, age):
print(f"name: {name}, age: {age}")
student_info(age=39, name="Mohammed")

# ATM System Project

def check_balance(balance):
print(f"Your current balance is rupees {balance}")

def withdraw(balance, amount):
if amount > balance:
print("Insufficient balance")
return balance
else:
balance = balance - amount
print(f"Withdraw successful & new balance: rupees {balance}")
return balance

def deposit(balance, amount):
balance = balance + amount
print(f"Deposit successful and new balance is: rupees {balance}")
return balance

def atm():
balance = 10000
print("Welcome to the ATM")

while True:
print("\nChoose option:")
print("1. Check balance")
print("2. Withdraw money")
print("3. Deposit money")
print("4. Exit")
choice = input("Enter your choice (1-4): ")
if choice == "1":
check_balance(balance)
elif choice == "2":
amount = float(input("Enter amount to withdraw: Rupees "))
balance = withdraw(balance, amount)
elif choice == "3":
amount = float(input("Enter amount to deposit: Rupees "))
balance = deposit(balance, amount)
elif choice == "4":
print("Exit, Goodbye")
break
else:
print("Invalid choice")
atm()

# Mini project on calculator:

def add(x, y):
return x + y
def subtraction(x, y):
return x - y
def multiply(x, y):
return x * y
def divide(x, y):
if y == 0:
return "Cannot divide zero"
return x / y
print("Addition:", add(3, 6))
print("Subtraction:", subtraction(8, 5))
print("Multiplication:", multiply(11, 3))
print("Division:", divide(10, 5))