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