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functools_cached_property_38.py
64 lines (54 loc) 路 2.34 KB
/
functools_cached_property_38.py
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from __future__ import annotations
from threading import RLock
from typing import Any, Callable, Generic, TypeVar, overload
__all__ = ["cached_property"]
_NOT_FOUND = object()
_T = TypeVar("_T")
class cached_property(Generic[_T]):
def __init__(self, func: Callable[[Any], _T]):
self.func = func
self.attrname: str | None = None
self.__doc__ = func.__doc__
self.lock = RLock()
def __set_name__(self, owner: type[Any], name: str) -> None:
if self.attrname is None:
self.attrname = name
elif name != self.attrname:
msg = f"Cannot assign the same cached_property to two different names ({self.attrname!r} and {name!r})."
raise TypeError(msg)
@overload
def __get__(self, instance: None, owner: type[Any] | None = ...) -> cached_property[_T]:
...
@overload
def __get__(self, instance: object, owner: type[Any] | None = ...) -> _T:
...
def __get__(self, instance: object | None, owner: type[Any] | None = None) -> Any:
if instance is None:
return self
if self.attrname is None:
msg = "Cannot use cached_property instance without calling __set_name__ on it."
raise TypeError(msg)
try:
cache = instance.__dict__
except AttributeError: # not all objects have __dict__ (e.g. class defines slots)
msg = (
f"No '__dict__' attribute on {type(instance).__name__!r} "
f"instance to cache {self.attrname!r} property."
)
raise TypeError(msg) from None
val = cache.get(self.attrname, _NOT_FOUND)
if val is _NOT_FOUND:
with self.lock:
# check if another thread filled cache while we awaited lock
val = cache.get(self.attrname, _NOT_FOUND)
if val is _NOT_FOUND:
val = self.func(instance)
try:
cache[self.attrname] = val
except TypeError:
msg = (
f"The '__dict__' attribute on {type(instance).__name__!r} instance "
f"does not support item assignment for caching {self.attrname!r} property."
)
raise TypeError(msg) from None
return val