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Cachetools timer with datetime.now #8459
Description
A followup to the issue presented in #6953, I'm running into mypy errors when implementing a cache using the mechanism as defined in the cachetools documentation.
Cachetools documentation for TRLUCache with example that matches the implementation below.
My implementation
def expires_in_ttu(_key, value, now):
expires_in = value[1]
return now + timedelta(seconds=expires_in)
cache = TLRUCache(maxsize=10, ttu=expires_in_ttu, timer=datetime.now)
The mypy error:
Argument "timer" to "TLRUCache" has incompatible type "Callable[[Optional[tzinfo]], datetime]"; expected "Callable[[], float]"
Workaround:
We can use time.monotonic instead of datetime.now, but:
- the example in the docs use datetime.now
- datetime.now is arguably more familiar to most developers
Versions
- cachetools: 5.2.0
- types-cachetools: 5.2.1
Activity
Akuli commentedon Aug 1, 2022
Arguably
time.monotonic()would be better for some applications, becausedatetime.now()can go backwards. But I agree that both should be supported.michaeljpeake commentedon Apr 18, 2023
I've have a similar problem with the
ttlvariable. Maybe my own incompetance but I couldn't get my tests with freezegun working withtime.monotonic. Made the switch and can write the tests no problem but currently haven't to supress lint warnings for usingtimedeltainstead of float.