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cachetools memoizing attributes (cache, key, lock) are not available #13395
Description
According to cachetools’ documentation,
The decorator’s cache, key and lock parameters are also available as
cache,cache_keyandcache_lockattributes of the memoizing wrapper function. […] For the common use case of clearing or invalidating the cache, the decorator also provides acache_clear()[.]
However, this is currently not reflected in the typeshed stubs. cached() and cachedmethod() are declared to return IdentityFunction, i.e. a decorator that takes the function-to-be-cached and returns a callable with identical signature, without the additional properties and functions. It would be great if support for this was added.
Code example
import cachetools
import threading
## cached function
@cachetools.cached(cache=cachetools.LRUCache(maxsize=10),
key=lambda x, y: y,
lock=threading.Lock())
def fun(x: str, y: str) -> str:
return y
print(fun('ignored', 'hello world'))
with fun.cache_lock:
print(fun.cache[fun.cache_key('ignored', 'hello world')])
fun.cache_clear()
## cached method
class Class:
def __init__(self):
self.cache = cachetools.LRUCache(maxsize=10)
self.lock = threading.Lock()
@cachetools.cachedmethod(cache=lambda self: self.cache,
key=lambda self, x, y: y,
lock=lambda self: self.lock)
def meth(self, x: str, y: str) -> str:
return y
c = Class()
print(c.meth('ignored', 'hello world'))
with c.meth.cache_lock(c):
print(c.meth.cache(c)[c.meth.cache_key(c, 'ignored', 'hello world')])I’m not sure if this is the “intended” way to use the memoizing attributes of a cached method (passing in c for the self argument explicitly), but it seems to work at runtime, at least. (Personally, I’d be fine with support just for @cached functions, but I figured it makes sense to include @cachedmethod in the example too.)
Activity
lucaswerkmeister commentedon Jan 12, 2025
I tried to implement this myself, but I’m afraid I’m not good enough at Python generics and type magic, sorry 😔 but maybe someone else can figure it out!
max-muoto commentedon Jan 27, 2025
I think the core reasons why this is difficult to do (at least for
cachedmethod) are the same as whylru_cachein the stdlib isn't properly typed: #11280 and https://discuss.python.org/t/allow-self-I think fixing
cachedtools.cachedwouldn't be too hard, something like this would work for the example you provided:(Ignoring the
cachetype)tqa236 commentedon Oct 24, 2026
I think this issue is fixed by #15657 (and before that, #14770)