def backoff_delay()

in scripts/util.py [0:0]

• 19 lines of code
• 12 McCabe index (conditional complexity)

def backoff_delay(start, timeout=None, ratio=None, count: int = 0):
    """generates `count` waits starting at `start`
    sum of waits is `timeout` or each one is `ratio` bigger than the last
    the last wait is always 0"""
    # timeout or ratio must be set but not both
    assert (timeout is None) ^ (ratio is None)
    assert ratio is None or ratio > 0
    assert timeout is None or timeout >= start
    assert (count > 1 or timeout is not None) and isinstance(count, int)
    assert start > 0

    if count == 0:
        # Equation for auto-count is tuned to have a max of
        # ~int(timeout) counts with a start wait of <0.01.
        # Increasing start wait decreases count eg.
        # backoff_delay(10, timeout=60) -> count = 5
        count = int(
            (timeout / ((start + 0.05) ** (1 / 2)) + 2) // math.log(timeout + 2)
        )

    yield start
    # if ratio is set:
    # timeout = start * (1 - ratio**(count - 1)) / (1 - ratio)
    if ratio is None:
        ratio = find_ratio(start, count - 1, timeout)

    wait = start
    # we have start and 0, so we only need to generate count - 2
    for _ in range(count - 2):
        wait *= ratio
        yield wait
    yield 0
    return