Repeating with while

Stirring a sauce: while the sauce is still runny, keep stirring. You don’t decide in advance how many stirs; you check after every stir. The moment it’s thick, you stop.

That’s a while loop. It’s for when you don’t know how many times you’ll need to repeat something, only when to stop.

But beware the cursed recipe: “while the sauce is runny, stir,” with the stove turned off. The sauce never thickens and you stir forever. That’s an infinite loop, the most famous bug in programming.

The real words

while condition:
    # the loop body: runs again and again
    # while condition is True
# runs once the condition is False

• Each trip through the body is called an iteration.
• The condition is checked before every iteration. If it’s False the very first time, the body never runs at all.
• A infinite loop happens when nothing in the body ever makes the condition False. Fix it by making sure each round makes progress toward stopping.
• break jumps out of the loop immediately. while True: with a break inside is a common way to write “keep going until something happens.”

Three classic patterns:

1. Counter: start at 0, add 1 each round, stop at a limit.
2. Goal-seeking: repeat until a value reaches a target (savings reach $1,000).
3. Sentinel: keep reading input until a special sentinel value like "quit" or 0 appears.