Python While Loops

What is a While Loop in Python?

A while loop executes a block of code as long as a specified condition evaluates to True. It checks the condition at the beginning of each iteration.

Why Use While Loops?

1. Repetition Without Knowing Exact Iterations: When you don’t know in advance how many times a block of code should execute.
2. Dynamic Exit Conditions: Based on runtime input or program state.
3. Efficient Iterative Tasks: Perform operations like counting, processing data or validating inputs.

Syntax of a While Loop

while condition:
    # Code to execute as long as the condition is True

• condition: A boolean expression. The loop runs until this evaluates to False.
• Indentation: The code block inside the loop must be indented.

Example: Basic While Loop

count = 1
while count <= 5:
    print("Count is:", count)
    count += 1

Output:

csharpCopy codeCount is: 1  
Count is: 2  
Count is: 3  
Count is: 4  
Count is: 5  

Using Else with While Loops

Python allows an optional else block with a while loop. The else block executes after the loop ends, provided the condition becomes False and the loop wasn’t terminated by a break statement.

Example:

number = 3
while number > 0:
    print("Number:", number)
    number -= 1
else:
    print("Loop ended naturally.")

Output:

vbnetCopy codeNumber: 3  
Number: 2  
Number: 1  
Loop ended naturally.  

Common Operations in While Loops

1. Infinite Loops:

A while loop can run indefinitely if the condition never becomes False. Use infinite loops with caution and always include a way to break out.

Example:

while True:
    user_input = input("Type 'exit' to stop: ")
    if user_input.lower() == "exit":
        print("Exiting the loop.")
        break

2. Using Break Statement:

The break statement exits the loop immediately, even if the condition is still True.

Example:

count = 0
while count < 10:
    print(count)
    count += 1
    if count == 5:
        print("Loop terminated early.")
        break

3. Using Continue Statement:

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

Example:

count = 0
while count < 5:
    count += 1
    if count == 3:
        print("Skipping 3.")
        continue
    print("Current count:", count)

Output:

Current count: 1  
Current count: 2  
Skipping 3.  
Current count: 4  
Current count: 5  

Practical Examples of While Loops

Example 1: Countdown Timer

import time

countdown = 5
while countdown > 0:
    print("Countdown:", countdown)
    countdown -= 1
    time.sleep(1)  # Adds a 1-second delay
print("Blastoff!")

Example 2: User Input Validation

while True:
    age = input("Enter your age (number only): ")
    if age.isdigit():
        print("Thank you!")
        break
    else:
        print("Invalid input. Please try again.")

Example 3: Summing Numbers Until Zero

total = 0
while True:
    num = int(input("Enter a number (0 to stop): "))
    if num == 0:
        break
    total += num
print("Total sum is:", total)

Best Practices for Using While Loops

1. Set Clear Exit Conditions: Always ensure your loop has a defined stopping point.
2. Minimize Infinite Loops: Use infinite loops sparingly and always include break statements.
3. Validate Input: When using while loops for input validation, check all possible edge cases.