while Loop in Python: Trace a Bounded Retry Simulation

Start with a small, explicit task

Simulate readiness using a fixed list of boolean outcomes. Count attempts starting at one, stop after a success, and otherwise report exhausted. The inputs are a local teaching fixture; the script does not call a service, wait between attempts or suggest retrying every real failure.

Run the complete example

This original example was checked with Python 3.12.14. Save it as python_while_loop.py and run it with Python 3.12. It uses only the standard library. The assertions check the stated results.

def attempt(outcomes, limit):
    number = 0
    trace = []
    ready = False
    while number < limit and number < len(outcomes):
        ready = outcomes[number]
        number += 1
        trace.append(number)
        if ready:
            break
    return trace, "ready" if ready else "exhausted"
success = attempt([False, False, True, True], 3)
exhausted = attempt([False, False, True], 2)
assert success == ([1, 2, 3], "ready")
assert exhausted == ([1, 2], "exhausted")
assert attempt([True], 0) == ([], "exhausted")
print(success)
print(exhausted)

Explain the result

number begins at zero for indexing, then advances before its human-readable attempt number is recorded. The third outcome is reached when the limit is three, so success occurs on attempt three. With a limit of two, that same third outcome is never inspected. The zero-limit case performs no attempts, even though its first potential outcome is true.

The second condition also prevents indexing beyond the synthetic outcome list. Advancing number on every visited path is the key termination fact. An actual network operation would need its own failure classification and timeouts; this small control-flow model does not establish those policies.

Avoid these mistakes

Using <= instead of < can accidentally allow an extra iteration when the counter starts at zero. A continue placed before the increment can also prevent progress. Inspect every branch for a state change or an exit; do not run an intentionally infinite loop just to observe that it fails to terminate.