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74 lines
2.6 KiB
Python
74 lines
2.6 KiB
Python
# SPDX-License-Identifier: AGPL-3.0-or-later
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# lint: pylint
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# pyright: basic
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"""Module for backward compatibility.
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"""
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# pylint: disable=C,R
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__all__ = ('cached_property',)
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try:
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from functools import cached_property # type: ignore
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except ImportError:
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# cache_property has been added in py3.8 [1]
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#
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# To support cache_property in py3.7 the implementation from 3.8 has been
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# copied here. This code can be cleanup with EOL of py3.7.
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#
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# [1] https://docs.python.org/3/library/functools.html#functools.cached_property
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from threading import RLock
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_NOT_FOUND = object()
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class cached_property:
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def __init__(self, func):
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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.lock = RLock()
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def __set_name__(self, owner, name):
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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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def __get__(self, instance, owner=None):
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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("Cannot use cached_property instance without calling __set_name__ on it.")
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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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