retry.py

retry.py

#Copyright 2021 Fabian Bosler

# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation 
# files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, 
# modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom 
# the Software is furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all copies or substantial portions of the 
# Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO 
# THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS 
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from functools import wraps
import time
import logging
import random

logger = logging.getLogger(__name__)


def retry(exceptions, total_tries=4, initial_wait=0.5, backoff_factor=2, logger=None):
    """
    calling the decorated function applying an exponential backoff.
    Args:
        exceptions: Exception(s) that trigger a retry, can be a tuple
        total_tries: Total tries
        initial_wait: Time to first retry
        backoff_factor: Backoff multiplier (e.g. value of 2 will double the delay each retry).
        logger: logger to be used, if none specified print
    """
    def retry_decorator(f):
        @wraps(f)
        def func_with_retries(*args, **kwargs):
            _tries, _delay = total_tries + 1, initial_wait
            while _tries > 1:
                try:
                    log(f'{total_tries + 2 - _tries}. try:', logger)
                    return f(*args, **kwargs)
                except exceptions as e:
                    _tries -= 1
                    print_args = args if args else 'no args'
                    if _tries == 1:
                        msg = str(f'Function: {f.__name__}\n'
                                  f'Failed despite best efforts after {total_tries} tries.\n'
                                  f'args: {print_args}, kwargs: {kwargs}')
                        log(msg, logger)
                        raise
                    msg = str(f'Function: {f.__name__}\n'
                              f'Exception: {e}\n'
                              f'Retrying in {_delay} seconds!, args: {print_args}, kwargs: {kwargs}\n')
                    log(msg, logger)
                    time.sleep(_delay)
                    _delay *= backoff_factor

        return func_with_retries
    return retry_decorator


def log(msg, logger=None):
    if logger:
        logger.warning(msg)
    else:
        print(msg)


def test_func(*args, **kwargs):
    rnd = random.random()
    if rnd < .2:
        raise ConnectionAbortedError('Connection was aborted :(')
    elif rnd < .4:
        raise ConnectionRefusedError('Connection was refused :/')
    elif rnd < .8:
        raise ConnectionResetError('Guess the connection was reset')
    else:
        return 'Yay!!'


if __name__ == '__main__':
    # wrapper = retry((ConnectionAbortedError), tries=3, delay=.2, backoff=1, logger=logger)
    # wrapped_test_func = wrapper(test_func)
    # print(wrapped_test_func('hi', 'bye', hi='ciao'))

    wrapper_all_exceptions = retry(Exception, total_tries=2, logger=logger)
    wrapped_test_func = wrapper_all_exceptions(test_func)
    print(wrapped_test_func('hi', 'bye', hi='ciao'))

@NicholasBallard thank you! Your kind words are much appreciated!

Thanks for sharing this. It was very useful

Elegant solution, thanks you!

First - AWESOME! I sure gonna use this one.

In the docstring: "exceptions: Exeption(s) that trigger a retry, can be a tuble"
I guess you meant "tuple", right?

First - AWESOME! I sure gonna use this one.

In the docstring: "exceptions: Exeption(s) that trigger a retry, can be a tuble"
I guess you meant "tuple", right?

@liorbunzl Thanks so much! Appreciate it :)

Your comment made me laugh :) Had to think about bubbles. But jupp, ofc you are right. Thx for pointing it out.

Thanks for this code. Really helpful :)

One doubt, in line no 22, Is there any reason why you've set _tries = total_tries + 1. Can't it just be _tries= total_tries? And check while _tries > 0

Hi @FBosler,

I would like to reuse your code, do you have a open source license attached to it?

Hi @FBosler,

I would like to reuse your code, do you have a open source license attached to it?

@arthur-c Sure I added it :)

Thank you!

nice when you randomly stumble onto your ex-managers code