Your code looks fine to me.

For some nitpicks:

1. pass the exception to_save_exception to ensure you're interacting with the correct error, and
2. pass the path to the log file to the class, or change to alogging.Logger, to make logging to a different location easier to change.

It's likely to be irrelevant for most parameters, but I think thatself.nb_calls += 1 belongs in thetry block before calling the function rather than afinally block after.

To take a small example, consider@ExceptionMonitor(error_rate_threshold=0.5, min_calls=2)and function results like[success, success, exception]. I would argue that this does not clear the 50% threshold, however the code as written would say that it does.

This would also address@toolic's note about division by zero.

Since the code does a division calculation:

self.error_rate = self.nb_exceptions / self.nb_calls

it would be good to add a check that the divisor (nb_calls) is not 0. It is initialized to 0 by__init__:

self.nb_calls = 0

You might want to check thatmin_calls is greater than 0 as well, unless you want to support that case. If you do support 0, it might be worth explicitly documenting that.

• \$\begingroup\$Checkingnb_calls is unnecessary as long asmin_calls > 0, there is already a>= check. It would be better to only checkmin_calls in constructor IMO.\$\endgroup\$

  STerliakov

  – STerliakov

  2025-04-04 13:12:49 +00:00

  CommentedApr 4 at 13:12

One issue that I identified later:

The error rate calculation is cumulative, so error bursts will be missed. For example, if the error threshold is 0.05 (5%) andmin_calls is 10 and there are 8 consecutive exceptions from the 20th to the 27th call, the cumulative error rate will be 8/27 which is around 3%. Although technically correct, it's more useful to calculate the error rate within a sliding window, like this:

class ExceptionMonitor:    """Monitor the number of exceptions raised and the number of calls made to a function."""    def __init__(        self, error_rate_threshold: float, min_calls: int, window_sz: int = 100    ):        """        :param error_rate_threshold: The error rate threshold in [0,1), above which an exception is raised.        :param min_calls: The minimum number of calls before the error rate is calculated.        :param window_sz: The size of the sliding window for calculating exception rate.        """        self.error_rate_threshold = error_rate_threshold        self.min_calls = min_calls        self.exceptions_log = "exceptions.log"        if os.path.exists(self.exceptions_log):            os.remove(self.exceptions_log)        if window_sz < min_calls:            raise ValueError(                f"Window size {window_sz} must be greater than or equal to min_calls {min_calls}."            )        self.window_sz = window_sz        self.recent_outcomes = deque(maxlen=window_sz)    def _error_rate_exceeded(self):        if len(self.recent_outcomes) < self.min_calls:            return False        return (            sum(self.recent_outcomes) / len(self.recent_outcomes)        ) > self.error_rate_threshold    def _save_exception(self):        with open("exceptions.log", "a") as f:            f.write(f"{datetime.now()}\n")            f.write(traceback.format_exc())            f.write("\n\n")    def __call__(self, func):        @functools.wraps(func)        def wrapper(*args, **kwargs):            try:                result = func(*args, **kwargs)                self.recent_outcomes.append(False)                return result            except Exception:                self.recent_outcomes.append(True)                if self._error_rate_exceeded():                    raise                self._save_exception()        return wrapper

• \$\begingroup\$Nice self-answer +1\$\endgroup\$

  Peilonrayz

  – Peilonrayz♦

  2025-04-12 10:32:29 +00:00

  CommentedApr 12 at 10:32

• python
• error-handling