Python cocktail: mix a context manager and an iterator in equal parts

Summary:

The tenacity library comes with an intriguing mix of iterators and context managers to allow the users to retry blocks with this syntax:

    from tenacity import Retrying, stop_after_attempt

    for attempt in Retrying(stop=stop_after_attempt(3)):
        with attempt:
            1 / 0

You can use the same mechanism yourself, by creating and linking a custom context manager and iterator:

    class YouAndIhaveUnfinishedBusiness:
        def __init__(self, notify_success, attempt_number):
            self.notify_success = notify_success
            self.attempt = attempt_number

        def __enter__(self):
            pass

        def __exit__(self, exc_type, exc_value, traceback):
            if exc_value:
                print(f"You have disappointed me {self.attempt} time(s).")
            else:
                self.notify_success()
            return True

    class DoOrDoNotThereIsNoTry:
        def __init__(self, max_attempts):
            self.max_attempts = max_attempts
            self.success = False

        def __iter__(self):
            for i in range(self.max_attempts):
                yield YouAndIhaveUnfinishedBusiness(self.succeed, i+1)
                if self.success:
                    print("You are ready for the Kumite.")
                    break
            else:
                print("We trained him wrong on purpose, as a joke.")

        def succeed(self):
            self.success = True