Retry an action with exponential backoff

retry_with_backoff.py

"""Retry an action with exponential backoff.

Inspired by:
    - https://www.toptal.com/python/python-parameterized-design-patterns#classes-as-exceptions
    - https://stackoverflow.com/a/33577016/3775614
"""
# WARNING: Never used yet
# TODO: Add a unit test module

import time


class MaxAttemptsReached(Exception):
    """Raised when retry_with_backoff max attempt is reach."""

    def __init__(self, action, max_attempts):
        """MaxAttemptsReached
        
        Arguments:
            - action (callable): the attempted action
            - max_attempts (int): the number of attempts tried before faulting to this
        """
        self.message = "Max attempts {0} reached for action {1}".format(
            max_attempts, getattr(action, '__name__', repr(action))
        )
        super().__init__(self.message)


def retry_with_backoff(
        action,
        exceptions,
        max_attempts=10,
        attempts_so_far=0
):
    """Retry an action with exponential backoff.

    Attempt an action that could fail,
    and retry with exponential backoff,
    until a maximum number of attempts is reached.

    Arguments:
        - action (callable): The action to attempt
        - exceptions (Exception or tuple): Can be any exception
            or a tuple of exceptions to catch.
        - max_attempts (int): The maximum attempt to try,
            default: 10
        - attempts_so_far (int): The current number of attempts,
            mainly use for recursiveness,
            default: 0

    Returns:
        - the result of {action} if it succeed,
          or retries with a sleep time of {attempts_so_far ** 2}
    """
    try:
        return action()
    except exceptions:
        attempts_so_far += 1
        if attempts_so_far >= max_attempts:
            raise MaxAttemptsReached(action, max_attempts)
        else:
            time.sleep(attempts_so_far ** 2)
            return retry_with_backoff(
                action, exceptions, max_attempts, attempts_so_far
            )