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Exponential backoff decorator
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| import functools | |
| import time | |
| import logging | |
| logging.basicConfig(level=logging.DEBUG, format='%(message)s') | |
| logger = logging.getLogger(__name__) | |
| def retry(predicate=None, max_tries=3, max_delay=60, | |
| delay_s=1, exponential=False): | |
| if predicate is None: | |
| predicate = bool | |
| def decorator(f): | |
| def it(): | |
| def factor(p): | |
| if exponential: | |
| return pow(2, p) | |
| return 1 | |
| for p in range(max_tries): | |
| yield min(factor(p) * delay_s, max_delay) | |
| @functools.wraps(f) | |
| def wrapper(*args, **kwargs): | |
| last_e = None | |
| for delay in it(): | |
| try: | |
| result = f(*args, **kwargs) | |
| except BaseException as e: | |
| last_e = e | |
| logger.exception('error in retry decorator!') | |
| else: | |
| if predicate(result): | |
| return result | |
| logger.debug('retrying after {} seconds'.format(delay)) | |
| time.sleep(delay) | |
| if last_e: | |
| raise last_e | |
| raise Exception('No more retries!') | |
| return wrapper | |
| return decorator | |
| if __name__ == '__main__': | |
| def flaky(n_errors=0, max_tries=5, | |
| predicate=lambda _: True, exponential=True): | |
| n = {'errors': n_errors} | |
| @retry(max_tries=max_tries, | |
| predicate=predicate, exponential=exponential) | |
| def f(): | |
| if n['errors'] <= 0: | |
| return 'success!' | |
| n['errors'] -= 1 | |
| raise Exception('boom!') | |
| return f | |
| # within retry limit | |
| f = flaky(n_errors=3, max_tries=5) | |
| print(f()) | |
| # no more retries | |
| f = flaky(n_errors=3, max_tries=3) | |
| print(f()) |
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