While Loops in Python: Complete Guide with Examples

Quick answer: Learn Python while loops including syntax, break and continue, infinite loops, the while-else clause, and common interview questions.

Basic While Loop Syntax

count = 1

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

The condition is checked before each iteration. If it is false from the start, the loop body never runs at all.

Infinite Loops and How They Happen

count = 1
while count <= 5:
    print(count)
    # forgot to increment count -- this never stops

The most common cause of an accidental infinite loop is forgetting to update the variable the condition depends on.

Break and Continue in a While Loop

count = 0
while True:
    count += 1
    if count == 5:
        break        # exits the loop
    print(count)

count = 0
while count < 10:
    count += 1
    if count % 2 == 0:
        continue     # skips even numbers
    print(count)

The while-else Clause

Like a for loop, a while loop can have an else clause that runs only if the loop finishes normally, without a break.

count = 0
while count < 5:
    count += 1
else:
    print("Loop completed normally")   # this runs

A Practical Example: Input Validation

while True:
    age = input("Enter your age: ")
    if age.isdigit() and int(age) > 0:
        age = int(age)
        break
    print("Please enter a valid positive number")

This pattern, an infinite loop with an internal break, is common when you need to keep asking until valid input is received.

While vs For: When to Use Each

Use a for loop when iterating over a known sequence. Use a while loop when the number of repetitions depends on a condition that can only be evaluated as the program runs, such as waiting for valid user input or processing until a value crosses a threshold.

Common Interview Questions

When is a while loop preferred over a for loop?

When the number of iterations is not known in advance and depends on a runtime condition, rather than a fixed, known sequence.

How would you deliberately create an infinite loop with a controlled exit?

Use while True combined with a break statement triggered by a specific internal condition, a common pattern for input validation or event loops.