74 lines
2.8 KiB
Python
74 lines
2.8 KiB
Python
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from __future__ import annotations
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import sys
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from typing import Any, Generic, TypeVar, overload
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if sys.version_info >= (3, 12):
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from functools import cached_property
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else:
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# based on the code from Python 3.14:
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# https://github.com/python/cpython/blob/
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# 5507eff19c757a908a2ff29dfe423e35595fda00/Lib/functools.py#L1089-L1138
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# Copyright (C) 2006 Python Software Foundation.
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# vendored under the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2 because
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# prior to Python 3.12 cached_property used a threading.Lock, which makes
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# it very slow.
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_T_co = TypeVar("_T_co", covariant=True)
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_NOT_FOUND = object()
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class cached_property(Generic[_T_co]):
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def __init__(self, func: Callable[[Any, _T_co]]) -> None:
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self.func = func
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self.attrname = None
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self.__doc__ = func.__doc__
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self.__module__ = func.__module__
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def __set_name__(self, owner: type[any], name: str) -> None:
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if self.attrname is None:
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self.attrname = name
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elif name != self.attrname:
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raise TypeError(
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"Cannot assign the same cached_property to two different names "
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f"({self.attrname!r} and {name!r})."
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)
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@overload
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def __get__(self, instance: None, owner: type[Any] | None = None) -> Self: ...
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@overload
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def __get__(
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self, instance: object, owner: type[Any] | None = None
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) -> _T_co: ...
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def __get__(
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self, instance: object, owner: type[Any] | None = None
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) -> _T_co | Self:
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if instance is None:
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return self
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if self.attrname is None:
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raise TypeError(
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"Cannot use cached_property instance without calling __set_name__ on it."
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)
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try:
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cache = instance.__dict__
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except (
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AttributeError
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): # not all objects have __dict__ (e.g. class defines slots)
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msg = (
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f"No '__dict__' attribute on {type(instance).__name__!r} "
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f"instance to cache {self.attrname!r} property."
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)
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raise TypeError(msg) from None
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val = cache.get(self.attrname, _NOT_FOUND)
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if val is _NOT_FOUND:
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val = self.func(instance)
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try:
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cache[self.attrname] = val
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except TypeError:
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msg = (
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f"The '__dict__' attribute on {type(instance).__name__!r} instance "
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f"does not support item assignment for caching {self.attrname!r} property."
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)
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raise TypeError(msg) from None
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return val
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