"""Various helper functions."""
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import sys
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from collections.abc import Mapping
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from functools import cached_property
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from typing import Any, Callable, Generic, Optional, Protocol, TypeVar, Union, overload
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__all__ = ("under_cached_property", "cached_property")
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if sys.version_info >= (3, 11):
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from typing import Self
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else:
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Self = Any
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_T = TypeVar("_T")
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# We use Mapping to make it possible to use TypedDict, but this isn't
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# technically type safe as we need to assign into the dict.
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_Cache = TypeVar("_Cache", bound=Mapping[str, Any])
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class _CacheImpl(Protocol[_Cache]):
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_cache: _Cache
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class under_cached_property(Generic[_T]):
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"""Use as a class method decorator.
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It operates almost exactly like
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the Python `@property` decorator, but it puts the result of the
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method it decorates into the instance dict after the first call,
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effectively replacing the function it decorates with an instance
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variable. It is, in Python parlance, a data descriptor.
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"""
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def __init__(self, wrapped: Callable[[Any], _T]) -> None:
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self.wrapped = wrapped
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self.__doc__ = wrapped.__doc__
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self.name = wrapped.__name__
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@overload
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def __get__(self, inst: None, owner: Optional[type[object]] = None) -> Self: ...
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@overload
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def __get__(
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self, inst: _CacheImpl[Any], owner: Optional[type[object]] = None
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) -> _T: ...
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def __get__(
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self, inst: Optional[_CacheImpl[Any]], owner: Optional[type[object]] = None
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) -> Union[_T, Self]:
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if inst is None:
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return self
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try:
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return inst._cache[self.name] # type: ignore[no-any-return]
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except KeyError:
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val = self.wrapped(inst)
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inst._cache[self.name] = val
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return val
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def __set__(self, inst: _CacheImpl[Any], value: _T) -> None:
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raise AttributeError("cached property is read-only")
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