Retry with exponential backoff

retry.py

#!/usr/bin/env python3

from contextlib import contextmanager
import functools
import math
import signal
import time


class TimeoutException(Exception):
    pass


@contextmanager
def timeout(seconds):
    def signal_handler(signum, frame):
        raise TimeoutException(
            f"Timed out after {seconds} seconds")
    signal.signal(signal.SIGALRM, signal_handler)
    signal.alarm(seconds)
    try:
        yield
    finally:
        signal.alarm(0)


def retry(wait_exponential_multiplier=1, wait_exponential_max=60, stop_max_delay=240, stop_max_attempt_number=math.inf):
    """
    Retry with exponential backoff maxed at `wait_exponential_max`
    until either `stop_max_delay` or `stop_max_attempt_number` is reached

    Usage:
        @retry()
        some_unreliable_func():
            pass
    """
    def decorator(func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            last_error = None
            time_start = time.time()
            time_since_start = 0
            retry_count = 0
            try:
                with timeout(stop_max_delay):
                    while retry_count < stop_max_attempt_number:
                        try:
                            result = func(*args, **kwargs)
                        except Exception as e:
                            last_error = e
                            retry_count += 1
                            delay = min(wait_exponential_max,
                                        wait_exponential_multiplier * 2**(retry_count - 1))
                            print(
                                f"Error: {e}. Retrying in {delay} seconds...")
                            time.sleep(delay)
                        else:
                            return result
            except TimeoutException:
                pass
            time_since_start = time.time() - time_start
            raise Exception(
                f"Failed after {round(time_since_start, 2)}s, {retry_count} retries. Last error: {last_error}")
        return wrapper
    return decorator