Cachetools timer with datetime.now

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

Start by comparing the TLRUCache typing in types-cachetools with the documented datetime.now example and the behavior described in issue #6953. Reproduce the reported mypy error using the versions listed, then verify that the documented timer usage is accepted or that the documentation and typing agree.