Python While Loops Explained

A while loop repeats a block of code for as long as a condition stays true. You use it when you do not know in advance how many times you need to repeat.

count = 3

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

print("Go")

That prints 3, 2, 1, Go. Each pass checks the condition first, and stops the moment it is false.

How it actually runs#

Reading a while loop is easier if you say the steps out loud:

1. Check the condition.
2. If it is false, skip the whole block and carry on with the rest of the program.
3. If it is true, run the indented block.
4. Go back to step 1.

Note that the check happens before the first pass. If the condition is false to begin with, the body never runs at all:

count = 0

while count > 0:
    print("This never prints")

while or for?#

Ask yourself one question: can I say how many times before the loop starts?

If you can answer the question, use a for loop. If the stopping point depends on something that happens inside the loop, use while.

The infinite loop#

Everyone writes one. The cause is always the same: nothing inside the loop moves the condition towards being false.

count = 5

while count > 0:
    print(count)        # count never changes — this runs forever

The fix is a line that changes the thing being tested:

count = 5

while count > 0:
    print(count)
    count -= 1          # now it ends

Pattern 1: keep asking until the input is valid#

This is the most useful thing while loops do, and it is why they exist in most beginner programs.

while True:
    raw = input("Enter a number between 1 and 10: ")

    if not raw.isdigit():
        print("That is not a whole number.")
        continue

    number = int(raw)

    if number < 1 or number > 10:
        print("Out of range.")
        continue

    break        # everything passed — leave the loop

print("Thank you:", number)

while True loops forever on purpose, and break is the only way out. That is a normal, readable pattern — not a mistake — as long as there is a reachable break.

Pattern 2: a menu that runs until the user quits#

running = True

while running:
    print("\n1) Add   2) List   q) Quit")
    choice = input("Choice: ").strip().lower()

    if choice == "1":
        print("Adding...")
    elif choice == "2":
        print("Listing...")
    elif choice == "q":
        running = False
    else:
        print("Unknown choice.")

print("Goodbye.")

Using a running flag rather than break makes the exit condition visible at the top, which reads well once a menu grows.

break, continue and else#

n = 0

while n < 10:
    n += 1

    if n == 3:
        continue        # skip the rest of this pass
    if n == 6:
        break           # leave the loop entirely

    print(n)            # 1 2 4 5

Python also lets a while loop have an else, which runs only if the loop finished without hitting break:

attempts = 3

while attempts > 0:
    password = input("Password: ")
    if password == "letmein":
        print("Welcome")
        break
    attempts -= 1
else:
    print("Locked out.")

It is a neat way to say “what to do if we ran out rather than succeeded”.

Counting and accumulating#

total = 0
number = 1

while number <= 100:
    total += number
    number += 1

print(total)    # 5050

A for loop over range(1, 101) does the same job more clearly here — which is the point. Reach for while when the count is genuinely unknown, not to avoid learning range.

Waiting on something else#

A loop that spins as fast as the processor allows will pin a CPU core for no reason. If you are waiting for time to pass, sleep:

import time

seconds = 5

while seconds > 0:
    print(seconds)
    time.sleep(1)
    seconds -= 1

print("Done")

Where to go next#

• Python for loops — the other half of repetition
• Python try/except explained — handling bad input properly
• Build a number guessing game — a while loop doing real work