Method overrides with `@cachedmethod` do not pass type checks

[jvstme]

Describe the bug

If a subclass overrides a method of a parent class and decorates it with cachetools.cachedmethod, that override does not pass type checks (tested with pyright).

The issue was introduced in cachetools 7.1.0 and is also present in 7.1.1.

Reproduction steps

$ python --version
Python 3.14.4

$ pip install cachetools==7.1.1 pyright==1.1.409

$ cat repro.py
from cachetools import cachedmethod, TTLCache


class Parent:
    def some_method(self) -> int:
        return 0


class Child(Parent):
    def __init__(self) -> None:
        self._cache = TTLCache(maxsize=1, ttl=60)

    @cachedmethod(cache=lambda self: self._cache)
    def some_method(self) -> int:
        return 42

$ pyright -p repro.py

Expected result

$ pyright -p repro.py
0 errors, 0 warnings, 0 informations

Actual result

$ pyright -p repro.py
/tmp/repro/repro.py
  /tmp/repro/repro.py:14:9 - error: "some_method" overrides method of same name in class "Parent" with incompatible type "_cachedmethod_wrapper[int]" (reportIncompatibleMethodOverride)
1 error, 0 warnings, 0 informations

[tkem]

Thanks for reporting - interesting use case!

Previous versions of the typeshed stubs used

def cachedmethod(
    cache: Callable[[Any], MutableMapping[_KT, Any] | None],
    key: Callable[..., _KT] = ...,
    lock: Callable[[Any], AbstractContextManager[Any]] | None = None,
    condition: Condition | None = None,
) -> IdentityFunction: ...

which would make pyright complain when accessing the new wrapper attributes introduced in cachetools v7.0, e.g.

reveal_type(Child.some_method.cache)

[tkem]

After doing some research, I don't think there's a proper solution for this right now. Or, quoting python/typing#2128:

Callable protocols and their interaction with methods is fundamentally broken in Python currently.

So, at this time, I think your options are basically either

• Stick with cachetools and types-cachetools <7.0.0 and don't use any of the wrapper attributes.

or

• Suppress pyright errors at the call site, e.g.

@cachedmethod(cache=lambda self: self._cache)
def some_method(self) -> int:  # type: ignore[override]
    return 42