radowit/retrrry

Retry for Python3 using only standard library

Retrrry

Decorate flaky functions with @retry to apply retrying logic.

Simplest way to use retrrry is actually to copy the code in retry.py and use it in your project, since there is no dependencies other than the standard library.

@retry
def unreliable_func():
    import random
    if random.randint(0, 10) < 5:
        raise IOError('Fail')
    else:
        return 'Success'

Configurations

• Specify stop condition (i.e. limit by number of attempts)
• Specify wait condition (i.e. exponential backoff sleeping between attempts)
• Specify certain Exceptions
• Specify expected returned result

Installation

pip install retrrry

from retrrry import retry

Examples

The default behavior is to retry forever without waiting:

@retry
def never_stop_never_wait():
    print('Retry forever, ignore Exceptions, no wait between retries')
    raise Exception

Set the number of attempts before giving up:

@retry(stop_max_attempt_number=7)
def stop_after_7_attempts():
    print('Stopping after 7 attempts')
    raise Exception

Set a boundary for time for retry:

@retry(stop_max_delay=10000)
def stop_after_10_s():
    print('Stopping after 10 seconds')
    raise Exception

Set wait time between retries:

@retry(wait_fixed=2000)
def wait_2_seconds():
    print('Wait 2 second between retries')
    raise Exception

Inject some randomness:

@retry(wait_random_min=1000, wait_random_max=2000)
def wait_1_to_2_seconds():
    print('Randomly wait 1 to 2 seconds between retries')
    raise Exception

Use exponential backoff:

@retry(wait_exponential_multiplier=1000, wait_exponential_max=10000)
def wait_exponential_1000():
    print(
        'Wait 2^i * 1000 milliseconds after ith retry, up to 10 seconds, then 10 seconds afterwards'
    )
    raise Exception

Deal with specific exceptions:

def retry_if_io_error(exception):
    return isinstance(exception, IOError)

@retry(retry_on_exception=retry_if_io_error)
def might_have_io_error():
    print('Retry if an IOError occurs, raise any other errors')
    raise Exception

@retry(retry_on_exception=retry_if_io_error, wrap_exception=True)
def might_have_io_error_raise_retry_error():
    print('Retry if an IOError occurs, raise any other errors wrapped in RetryError')
    raise Exception

Alter the behavior of retry based on a function return value:

def retry_if_result_none(result):
    return result is None

@retry(retry_on_result=retry_if_result_none)
def might_return_none():
    print('Retry if return value is None')
    import random
    if random.randint(0, 10) > 1:
        return None
    return 'Done'

# Or retry if result is equal to 1
@retry(retry_on_result=lambda res: res == 1)
def might_return_one():
    print('Retry if return value is 1')
    import random
    if random.randint(0, 10) > 1:
        return 1
    return 0

Finally, we can always combine all of the configurations.