typing patterns for cached data results

[jvanasco]

The returned values of CacheRegion.get(key) and CacheRegion.get_or_create(key, generator_function) are typed as CachedValue and NoValue.

Trying to type the CachedValue in one of my projects is rather difficult because I utilize a proxy pattern. A stripped down description is the following:

CACHE_REGIONS: Dict[str, CacheRegion]: {"region1": region1CacheInstance}

class CacheProxyA():
     _cache_region = "region1"
    def guid_to_id(self, guid:str): 
       key = "guid2id:%s" % guid
       return CACHE_REGIONS[self._cache_region].get(key)

The issue is that I need to type the return value of the function as -> Union[NoValue, int], as various filters will deserialize/decode a cache hit into the int.

If I type the return value, so calling functions are correct, I get a type mismatch error:

error: Incompatible return value type (got "CachedValue | NoValue", expected "int | NoValue") 

If I don't type the return value, no issue there, but I lose the benefits of typing.

Does anyone have any ideas on possible solutions?

I know there is no perfect solution, as a lot of this is handled through configured dogpile filters/proxies that the typing system is oblivious to.

At the very least, I'd like to match the typing of the output (CacheRegion.get) with the typing of the input (the output of the function passed to CacheRegion.get_or_create).

[zzzeek]

we are working ont his over at https://gerrit.sqlalchemy.org/c/sqlalchemy/dogpile.cache/+/5270

[jvanasco]

Thanks, Mike. I'll follow that and start reading up on the changes.