A retry decorator which swallows exceptions until the retry limit is reached.

retry_decorator.py

import time
import math
import logging

retry_logger = logging.getLogger('retry_logger')

# Retry decorator with exponential backoff
def retry(tries, delay=3, backoff=2):
    '''Retries a function or method until it completes or the retry limit is reached.

    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

            while mtries > 0:
                try:
                    logging.info('Making attempt')
                    rv = f(*args, **kwargs)
                    return rv
                except Exception:
                    logging.info('Attempt failed')
                    mtries -= 1      # consume an attempt
                    logging.info('Delay of {0} seconds'.format(mdelay))
                    time.sleep(mdelay) # wait...
                    mdelay *= backoff  # make future wait longer

                    if not mtries:
                        logging.info('Out of retries.')
                        raise

            return None # Should never get here

        return f_retry
    return deco_retry

if __name__ == "__main__":
    # paltry testing
    logging.basicConfig(level=logging.INFO)

    times_to_fail = 5
    state_seed = [0] * times_to_fail + [1]
    state = (x for x in [0, 0, 0, 0, 0, 1])

    @retry(6, delay=1)
    def fail_then_succeed():
        if next(state):
            return 'Success!'
        else:
            #return 'Failure :('
            raise ValueError("Not Yet")

    print fail_then_succeed()