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- import functools
- from typing import Callable, TypeVar
- from typing_extensions import Concatenate, ParamSpec
- _P = ParamSpec("_P")
- _T = TypeVar("_T")
- _C = TypeVar("_C")
- # Sentinel used to indicate that cache lookup failed.
- _cache_sentinel = object()
- def cache_method(
- f: Callable[Concatenate[_C, _P], _T],
- ) -> Callable[Concatenate[_C, _P], _T]:
- """
- Like `@functools.cache` but for methods.
- `@functools.cache` (and similarly `@functools.lru_cache`) shouldn't be used
- on methods because it caches `self`, keeping it alive
- forever. `@cache_method` ignores `self` so won't keep `self` alive (assuming
- no cycles with `self` in the parameters).
- Footgun warning: This decorator completely ignores self's properties so only
- use it when you know that self is frozen or won't change in a meaningful
- way (such as the wrapped function being pure).
- """
- cache_name = "_cache_method_" + f.__name__
- @functools.wraps(f)
- def wrap(self: _C, *args: _P.args, **kwargs: _P.kwargs) -> _T:
- assert not kwargs
- if not (cache := getattr(self, cache_name, None)):
- cache = {}
- setattr(self, cache_name, cache)
- cached_value = cache.get(args, _cache_sentinel)
- if cached_value is not _cache_sentinel:
- return cached_value
- value = f(self, *args, **kwargs)
- cache[args] = value
- return value
- return wrap
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