Exception retry

retry.py

# Retry decorator with exponential backoff
def retry(tries, delay=3, backoff=2):
    """
    Retries a function or method if exception is raised.

    delay sets the initial delay in seconds, and backoff sets the factor by which
    the delay should lengthen after each failure. backoff must be greater than 1,
    or else it isn't really a backoff. tries must be at least 0, and delay
    greater than 0.
    """

    if backoff <= 1:
        raise ValueError("backoff must be greater than 1")

    tries = math.floor(tries)
    if tries < 0:
        raise ValueError("tries must be 0 or greater")

    if delay <= 0:
        raise ValueError("delay must be greater than 0")

    def deco_retry(f):
        def f_retry(*args, **kwargs):
            mtries, mdelay = tries, delay # make mutable
            completed = False

            while not completed:
                try:
                    return f(*args, **kwargs)
                except Exception:
                    if not mtries:
                        logger.error("No retries left")
                        raise
                    mtries -= 1      # consume an attempt
                    logger.debug("Attempt failed, retrying in {}secs. ({} retries left)".format(
                        int(mdelay), int(mtries)))
                    time.sleep(mdelay) # wait...
                    mdelay *= backoff  # make future wait longer
        return f_retry # true decorator -> decorated function
    return deco_retry  # @retry(arg[, ...]) -> true decorator