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# SPDX-License-Identifier: AGPL-3.0-or-later
# lint: pylint
# pyright: basic
"""Module for backward compatibility.
"""
# pylint: disable=C,R
__all__ = ('cached_property',)
try:
from functools import cached_property # type: ignore
except ImportError:
# cache_property has been added in py3.8 [1]
#
# To support cache_property in py3.7 the implementation from 3.8 has been
# copied here. This code can be cleanup with EOL of py3.7.
#
# [1] https://docs.python.org/3/library/functools.html#functools.cached_property
from threading import RLock
_NOT_FOUND = object()
class cached_property:
def __init__(self, func):
self.func = func
self.attrname = None
self.__doc__ = func.__doc__
self.lock = RLock()
def __set_name__(self, owner, name):
if self.attrname is None:
self.attrname = name
elif name != self.attrname:
raise TypeError(
"Cannot assign the same cached_property to two different names "
f"({self.attrname!r} and {name!r})."
)
def __get__(self, instance, owner=None):
if instance is None:
return self
if self.attrname is None:
raise TypeError("Cannot use cached_property instance without calling __set_name__ on it.")
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
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