🔁 Python Loops for Beginners: for and while Explained

Here's a concise and beginner-friendly explanation of Python for and while loops along with example programs.

In Python, loops are used to repeat a block of code multiple times. There are two main types of loops:

✅ for Loop

The for loop is used to iterate over a sequence (like a list, tuple, string, or range). It automatically picks the next item in the sequence for each iteration.

Syntax:

for variable in sequence:

# code to execute

#Print numbers from 1 to 5

for i in range(1, 6):

print(i)

OUTPUT:

1 2 3 4 5

#Loop through a list of fruits

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:

print(fruit)

Output:

apple

banana

cherry

while Loop

A while loop repeats as long as a condition is True. It's useful when you don't know ahead of time how many times you'll need to loop.

Syntax:

while condition:

# code to execute

#Print numbers from 1 to 5

i = 1

while i <= 5:

print(i)

i += 1

Output:

1 2 3 4 5

#User input until correct password

correct_password = "python123"

user_input = ""

while user_input != correct_password:

user_input = input("Enter password: ")

print("Access granted!")

🔁 for Loop Examples

#Calculate the sum of numbers from 1 to 100

total = 0

for i in range(1, 101):

total += i

print("Sum is:", total)

OUTPUT:

Sum is: 5050

#Print the multiplication table of a number

num = int(input("enter a number"))

for i in range(1, 11):

print(f"{num} x {i} = {num * i}")

OUTPUT:

enter a number 4

4 x 1 = 4

4 x 2 = 8

4 x 3 = 12

4 x 4 = 16

4 x 5 = 20

4 x 6 = 24

4 x 7 = 28

4 x 8 = 32

4 x 9 = 36

4 x 10 = 40

#Print even numbers from a list

numbers = [1, 4, 7, 10, 13, 16]

for num in numbers:

if num % 2 == 0:

print(num)

OUTPUT:

4 10 16

#Find the maximum number in a list

numbers = [3, 7, 2, 9, 5]

max_num = numbers[0]

for num in numbers:

if num > max_num:

max_num = num

print("Maximum number:", max_num)

OUTPUT:

Maximum number: 9

#Calculate the average of a list

numbers = [10, 20, 30, 40]

total = 0

for num in numbers:

total += num

average = total / len(numbers)

print("Average:", average)

OUTPUT:

Average: 25.0

#Print numbers and their squares

for i in range(1, 11):

print(f"{i}^2 = {i**2}")

OUTPUT:

1^2 = 1

2^2 = 4

3^2 = 9

4^2 = 16

5^2 = 25

6^2 = 36

7^2 = 49

8^2 = 64

9^2 = 81

10^2 = 100

#Nested loop – multiplication tables from 1 to 3

for i in range(1, 4):

print(f"Multiplication table for {i}")

for j in range(1, 6):

print(f"{i} x {j} = {i * j}")

print()

OUTPUT:

Multiplication table for 1

1 x 1 = 1

1 x 2 = 2

1 x 3 = 3

1 x 4 = 4

1 x 5 = 5

Multiplication table for 2

2 x 1 = 2

2 x 2 = 4

2 x 3 = 6

2 x 4 = 8

2 x 5 = 10

Multiplication table for 3

3 x 1 = 3

3 x 2 = 6

3 x 3 = 9

3 x 4 = 12

3 x 5 = 15

#Print all prime numbers from 1 to 50

for num in range(2, 51):

is_prime = True

for i in range(2, int(num ** 0.5) + 1):

if num % i == 0:

is_prime = False

break

if is_prime:

print(num, end=" ")

OUTPUT:

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

#Count vowels in a string

text = "Python is fun"

vowels = "aeiouAEIOU"

count = 0

for char in text:

if char in vowels:

count += 1

print("Number of vowels:", count)

OUTPUT:

Number of vowels: 3

#Reverse a string

text = "hello"

reversed_text = ""

for char in text:

reversed_text = char + reversed_text

print("Reversed:", reversed_text)

OUTPUT:

Reversed: olleh

#Print characters of a string with their index

word = "Python"

for index in range(len(word)):

print(f"Character at index {index} is {word[index]}")

OUTPUT:

Character at index 0 is P

Character at index 1 is y

Character at index 2 is t

Character at index 3 is h

Character at index 4 is o

Character at index 5 is n

#Convert all items in a list to uppercase

fruits = ["apple", "banana", "cherry"]

for i in range(len(fruits)):

fruits[i] = fruits[i].upper()

print(fruits)

OUTPUT:

['APPLE', 'BANANA', 'CHERRY'

while loop examples

#Guess the number game

secret_number = 7

guess = None

while guess != secret_number:

guess = int(input("Guess the number (1-10): "))

print("Congratulations! You guessed it!")

OUTPUT:

Guess the number (1-10): 5

Guess the number (1-10): 4

Guess the number (1-10): 7

Congratulations! You guessed it!

#Countdown timer

count = 5

while count > 0:

print(count)

count -= 1

print("Liftoff!")

OUTPUT:

5

4

3

2

1

Liftoff!

#Validate input until it's a digit

user_input = input("Enter a number: ")

while not user_input.isdigit():

user_input = input("Invalid input. Enter a number: ")

print("Thank you! You entered:", user_input)

OUTPUT:

Enter a number: a

Invalid input.

Enter a number: 3

Thank you! You entered: 3

#Find the factorial of a number

num = 5

factorial = 1

while num > 0:

factorial *= num

num -= 1

print("Factorial:", factorial)

OUTPUT:

Factorial: 120

#Keep asking until the user types "exit"

command = ""

while command.lower() != "exit":

command = input("Type 'exit' to quit: ")

print("Exited.")

Type 'exit' to quit: hi

Type 'exit' to quit: good morning

Type 'exit' to quit: exit

Exited.

#Sum positive numbers until a negative number is entered

total = 0

num = 0

while num >= 0:

num = int(input("Enter a number (negative to stop): "))

if num >= 0:

total += num

print("Total sum:", total)

OUTPUT:

Enter a number (negative to stop): 4

Enter a number (negative to stop): 10

Enter a number (negative to stop): 1

Enter a number (negative to stop): -10

Total sum: 15

#Print digits of a number one by one

num = 12345

while num > 0:

digit = num % 10

print(digit)

num = num // 10

OUTPUT:

5 4 3 2 1

#Sum digits of a number

num = 1234

total = 0

while num > 0:

total += num % 10

num //= 10

print("Sum of digits:", total)

OUTPUT:

Sum of digits: 10

#Reverse an integer

num = 1234

reversed_num = 0

while num > 0:

digit = num % 10

reversed_num = reversed_num * 10 + digit

num = num // 10

print("Reversed number:", reversed_num)

OUTPUT:

Reversed number: 4321

#Check if a number is a palindrome

num = int(input("Enter a number: "))

original = num

reverse = 0

while num > 0:

digit = num % 10

reverse = reverse * 10 + digit

num = num // 10

if original == reverse:

print("Palindrome!")

else:

print("Not a palindrome.")

OUTPUT:

Enter a number: 121

Palindrome!

#Repeat menu until user quits

choice = ""

while choice != "3":

print("1. Say Hello")

print("2. Say Goodbye")

print("3. Exit")

choice = input("Choose an option: ")

if choice == "1":

print("Hello!")

elif choice == "2":

print("Goodbye!")

OUTPUT:

1. Say Hello

2. Say Goodbye

3. Exit

Choose an option: 1

Hello!

1. Say Hello

2. Say Goodbye

3. Exit

Choose an option: 2

Goodbye!

1. Say Hello

2. Say Goodbye

3. Exit

Choose an option: 1

Hello!

1. Say Hello

2. Say Goodbye

3. Exit

Choose an option: 3

#Print powers of 2 less than 100

num = 1

while num < 100:

print(num)

num *= 2

OUTPUT:

1 2 4 8 16 32 64

#Count how many times a digit appears

number = 1123581123

digit = 1

count = 0

while number > 0:

if number % 10 == digit:

count += 1

number //= 10

print(f"Digit {digit} appears {count} times.")

OUTPUT:

Digit 1 appears 4 times.

#Simulate a login system with 3 tries

correct_password = "python123"

attempts = 0

success = False

while attempts < 3:

pwd = input("Enter password: ")

if pwd == correct_password:

success = True

break

attempts += 1

if success:

print("Login successful!")

else:

print("Access denied.")

OUTPUT:

Enter password: python

Enter password: python 123

Enter password: python12

Access denied.

#Repeat until user enters a palindrome word

while True:

word = input("Enter a word: ")

if word == word[::-1]:

print("Palindrome detected!")

break

else:

print("Try again.")

OUTPUT:

Enter a word: abc

Try again.

Enter a word: aba

Palindrome detected!

#Simulate a dice roll until you get a 6

import random

roll = 0

while roll != 6:

roll = random.randint(1, 6)

print("Rolled:", roll)

OUTPUT:

Rolled: 4

Rolled: 5

Rolled: 2

Rolled: 5

Rolled: 1

Rolled: 2

Rolled: 1

Rolled: 4

Rolled: 1

Rolled: 2

Rolled: 4

Rolled: 5

Rolled: 2

Rolled: 5

Rolled: 3

Rolled: 6

Kishore Babu Valluri

Senior Data Scientist | Freelance Consultant | AI/ML & GenAI Expert

With deep expertise in machine learning, artificial intelligence, and Generative AI, I work as a Senior Data Scientist, freelance consultant, and AI agent developer. I help businesses unlock value through intelligent automation, predictive modeling, and cutting-edge AI solutions.