A Python decorator to cache functions and clear the cache as scheduled

cache_with_schedule.py

from datetime import datetime as dt
from croniter import croniter
from functools import wraps
from typing import Dict, Any


def cache_with_schedule(schedule: str):
    """
    Decorator to cache the results of a function "f(x)" and clear the cache as
    scheduled.

    -> "schedule" is a cron-like string.
    -> a "dict" is used as cache, so "x" needs to be hashable.

    Example:

    # "func" is invoked at most once in a minute.
    @cache_with_schedule("*/1 * * * *")
    def func(n):
        print("I was invoked")
        return {"a": n, "b": 20}
    """
    nowfn = dt.utcnow
    cron = croniter(schedule, nowfn())
    cache: Dict[Any, Any] = dict()

    def has_expired() -> bool:
        """
        Returns "True" if the cache has expired.
        """
        now = nowfn()
        has_expired = False
        while now > cron.get_next(dt):
            has_expired = True
        # Rewind one step to get the correct "next" date-time next time
        # "has_expired" is invoked.
        cron.get_prev(dt)
        return has_expired

    def decorator(f):
        @wraps(f)
        def wrapper(arg):
            nonlocal cache
            cache = dict() if has_expired() else cache
            res = cache[arg] if arg in cache else f(arg)
            cache[arg] = res
            return res

        return wrapper

    return decorator