Python while Loops

What Is a while Loop?

A while loop repeatedly executes a block of code as long as a specified condition is True.

Unlike a for loop, which is commonly used when iterating over a known sequence, a while loop is useful when repetition depends on a condition.

count = 1

while count <= 5:
    print(count)
    count += 1

1
2
3
4
5

The loop continues while count <= 5 remains true. Once count becomes 6, the condition becomes false and the loop stops.

Why Use while?

A while loop is especially useful when you do not know exactly how many times a task needs to repeat.

Common situations include:

• Waiting for valid user input.
• Repeating a menu until the user chooses Exit.
• Running a process while a condition is true.
• Retrying an operation.
• Creating game loops.
• Counting until a target is reached.
• Monitoring a changing condition.

Basic Syntax

The basic structure of a Python while loop is:

while condition:
    # code to execute

The condition must produce a Boolean result: True or False.

number = 1

while number <= 3:
    print("Hello")
    number += 1

Hello
Hello
Hello

The variable is updated during every iteration so that the condition eventually becomes false.

The Loop Condition

The condition controls whether the loop continues.

temperature = 30

while temperature > 25:
    print("Temperature is high")
    temperature -= 1

Temperature is high
Temperature is high
Temperature is high
Temperature is high
Temperature is high

The loop runs while the temperature is greater than 25. Once it reaches 25, the condition becomes false.

Counter-Controlled Loops

One of the simplest uses of a while loop is counting.

count = 1

while count <= 5:
    print(count)
    count += 1

Here, count is called a loop control variable.

Updating the Variable

One of the most important rules of a while loop is to make sure the condition can eventually become false.

number = 0

while number < 5:
    print(number)
    number += 1

The expression number += 1 increases the variable by one after every iteration.

Increment by Another Amount

number = 2

while number <= 10:
    print(number)
    number += 2

2
4
6
8
10

Counting Backwards

A while loop can also count downward.

count = 5

while count >= 1:
    print(count)
    count -= 1

print("Go!")

5
4
3
2
1
Go!

The operator -= decreases the value of count by one during each iteration.

while with User Input

One of the most practical uses of a while loop is repeatedly asking the user for input until a particular condition is satisfied.

answer = ""

while answer != "yes":
    answer = input("Enter yes to continue: ")

print("Thank you!")

The program keeps asking the user until they enter yes.

Menu Example

choice = ""

while choice != "3":

    print("1. View Profile")
    print("2. Settings")
    print("3. Exit")

    choice = input("Choose an option: ")

print("Program closed.")

Input Validation with while

A loop can force a program to continue asking for input until the user provides valid information.

age = int(input("Enter your age: "))

while age < 0:
    print("Age cannot be negative.")
    age = int(input("Enter your age again: "))

print("Age accepted:", age)

Range Validation

marks = int(input("Enter marks: "))

while marks < 0 or marks > 100:
    print("Marks must be between 0 and 100.")
    marks = int(input("Enter marks again: "))

print("Valid marks:", marks)

Using break

The break statement immediately terminates the loop.

number = 1

while number <= 10:

    if number == 5:
        break

    print(number)
    number += 1

1
2
3
4

When number becomes 5, break stops the loop immediately.

Using continue

The continue statement skips the rest of the current iteration and moves to the next iteration.

number = 0

while number < 6:

    number += 1

    if number == 3:
        continue

    print(number)

1
2
4
5
6

When the number becomes 3, continue skips the print() statement for that iteration.

while with else

Python allows an else block to be attached to a while loop.

The else block runs when the loop finishes normally because its condition becomes false.

count = 1

while count <= 3:
    print(count)
    count += 1

else:
    print("Loop finished.")

1
2
3
Loop finished.

When break Is Used

count = 1

while count <= 5:

    if count == 3:
        break

    print(count)
    count += 1

else:
    print("Loop finished.")

1
2

Because break terminated the loop, the else block did not run.

Nested while Loops

A nested loop is a loop placed inside another loop.

row = 1

while row <= 3:

    column = 1

    while column <= 3:
        print(row, column)
        column += 1

    row += 1

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3

For every iteration of the outer loop, the inner loop runs completely.

Infinite Loops

An infinite loop is a loop that never reaches a condition that makes it stop.

number = 1

while number <= 5:
    print(number)

This loop never changes number. Therefore, number <= 5 remains true forever.

Correct Version

number = 1

while number <= 5:
    print(number)
    number += 1

Intentional Infinite Loops

Infinite loops are sometimes intentional. For example, a continuously running application may use:

while True:

    command = input("Enter command: ")

    if command == "exit":
        break

In this pattern, break provides the exit condition.

Practical Real-World Examples

Example 1 — Countdown Timer Logic

seconds = 5

while seconds > 0:
    print("Seconds remaining:", seconds)
    seconds -= 1

print("Time's up!")

Seconds remaining: 5
Seconds remaining: 4
Seconds remaining: 3
Seconds remaining: 2
Seconds remaining: 1
Time's up!

Example 2 — Password Attempts

correct_password = "python123"

attempts = 3

while attempts > 0:

    password = input("Enter password: ")

    if password == correct_password:
        print("Login successful.")
        break

    attempts -= 1
    print("Incorrect password.")

else:
    print("Account temporarily locked.")

This example combines a loop, condition, counter and break to create a simple authentication flow.

Example 3 — Shopping Cart Menu

total = 0
choice = ""

while choice != "3":

    print("\n1. Add Rs. 500")
    print("2. Add Rs. 1000")
    print("3. Checkout")

    choice = input("Choose: ")

    if choice == "1":
        total += 500

    elif choice == "2":
        total += 1000

print("Total:", total)

Example 4 — Find a Number

numbers = [10, 25, 40, 55, 70]

index = 0
found = False

while index < len(numbers):

    if numbers[index] == 40:
        found = True
        break

    index += 1

print("Found:", found)

Found: True

Common Mistakes

1. Forgetting the Colon

while count < 5
    print(count)

Python requires a colon after the loop condition.

2. Forgetting to Update the Control Variable

count = 1

while count <= 5:
    print(count)

The value of count never changes, so the loop never ends.

3. Updating in the Wrong Direction

count = 5

while count > 0:
    print(count)
    count += 1

Here the value increases instead of decreasing, so the condition will remain true.

4. Incorrect Indentation

count = 1

while count <= 5:
print(count)
count += 1

The statements belonging to the loop must be indented.

5. Accidentally Creating an Infinite Loop with continue

Practice Exercises

Mini Challenge — Number Guessing Game

Build a simple number guessing game using a while loop.

Your program should:

1. Choose a secret number.
2. Ask the user to guess it.
3. Tell the user whether the guess is too high or too low.
4. Continue asking until the correct number is entered.
5. Count the number of attempts.
6. Display a success message at the end.

secret_number = 42

guess = 0
attempts = 0

while guess != secret_number:

    guess = int(input("Guess the number: "))

    attempts += 1

    if guess < secret_number:
        print("Too low!")

    elif guess > secret_number:
        print("Too high!")

    else:
        print("Correct!")

print("Attempts:", attempts)

Quick Knowledge Check

Lesson Summary

A Python while loop repeatedly executes code as long as its condition remains true.

• A while loop is controlled by a condition.
• The condition is checked before each iteration.
• The loop should normally contain a way for the condition to change.
• Counter variables are commonly used with while.
• break immediately terminates a loop.
• continue skips the current iteration.
• while...else can detect normal completion.
• Nested while loops can solve more complex problems.
• Input validation is a practical use of while.
• Always be careful about accidentally creating infinite loops.