while keeps going until the condition flips

A for loop runs once per item in a collection. That's the right shape when you have a known list of things — three users, ten files, five rows. But sometimes you don't know how many times the loop will run. You want it to keep going until something happens:

• Keep retrying until the API responds.
• Loop until the user types quit.
• Pop messages off the queue until it's empty.

For all of those, AI reaches for while. The first cousin of for, and a slightly more dangerous one.

The mental model: a condition checked at the top of every pass

while count > 0:
    print(f"countdown: {count}")
    count -= 1

A while loop runs in three phases, like for, but the order is different:

1. Check the condition. Right at the top, Python evaluates `count

   0. If True, run the body. If False`, skip the body and exit the loop.

2. Run the body. All the indented lines fire, in order.
3. Loop back to the top. Re-check the condition. Repeat.

The condition is only checked at the top. If the body changes something halfway through, the loop doesn't notice until the next iteration begins.

A worked example

The editor on the right counts down from 3:

Pass	count is...	Condition?	Body output	Body changes
1	3	True	countdown: 3	count = 2
2	2	True	countdown: 2	count = 1
3	1	True	countdown: 1	count = 0
4	0	False	(skipped — loop ends)	—

After the loop ends, the script moves on to print("liftoff").

The key move: count -= 1. Without that line, the condition never changes, and the loop runs forever. We need to talk about that.

The infinite-loop trap

A while loop has no built-in stopping point. The loop only ends when the condition flips false. If the body never moves toward false, the loop runs forever — until you kill the process or the browser tab freezes.

count = 3
while count > 0:
    print("forever")     # NO update to count — INFINITE LOOP

Don't run that one. The shape is identical to a working countdown, minus the count -= 1. That's one missing line between "works fine" and "your script never terminates."

Where AI specifically gets while wrong

Two patterns to watch for in code Cursor writes:

1. The "wait for the API" loop with no exit. AI sometimes writes while not response: and then doesn't put a sleep, a retry counter, or a bail-out inside. If the API never responds, you have a tight infinite loop hammering the network. Real production while loops should always have a maximum iteration count or a timeout.

2. while True: without a break. This is a legitimate pattern — "loop forever, until something inside says stop" — but it's only safe if there's an unmissable break somewhere in the body. Cursor sometimes writes while True: and then guards the break with a condition that's never true, producing an infinite loop disguised as a finite one.

When you see while in AI code, your first reading habit should be: "what changes inside the body to eventually flip the condition, and am I sure that change actually happens?" If you can't answer, the loop is probably broken.

Run the editor. Three iterations, then liftoff.