Henry SchreinerandJoe Rickerby
d6dc3b7cd9
* chore: add PyLint and fix most issues * fix: minor fixes after first push * chore: remove reference to old toml lib * chore: minor options cleanup * ci: only fail with many pylint issues, annotate in GHA * refactor: address review * ci: force nox to report in CI * refactor: use map instead of if chain * refactor: simpler shell_with_arch * refactor: even simpler shell_with_arch * Restore if...elif...else blocks where guard-style is not intended Co-authored-by: Joe Rickerby <joerick@mac.com>
66 lines
2.4 KiB
Python
66 lines
2.4 KiB
Python
from threading import RLock
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from typing import Any, Callable, Generic, Optional, Type, TypeVar, overload
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__all__ = ["cached_property"]
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_NOT_FOUND = object()
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_T = TypeVar("_T")
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class cached_property(Generic[_T]):
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def __init__(self, func: Callable[[Any], _T]):
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self.func = func
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self.attrname: Optional[str] = None
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self.__doc__ = func.__doc__
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self.lock = RLock()
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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: Optional[Type[Any]] = ...) -> "cached_property[_T]":
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...
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@overload
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def __get__(self, instance: object, owner: Optional[Type[Any]] = ...) -> _T:
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...
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def __get__(self, instance: Optional[object], owner: Optional[Type[Any]] = None) -> Any:
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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 AttributeError: # 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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with self.lock:
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# check if another thread filled cache while we awaited lock
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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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