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