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bpo-21145: Add cached_property decorator in functools #6982

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Merged
ncoghlan merged 12 commits into from
Aug 28, 2018
+256 −0
Merged

bpo-21145: Add cached_property decorator in functools #6982

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bpo-21145: Add cached_property decorator in functools
carljm May 19, 2018
72259cd
Review feedback.
carljm May 20, 2018
26f3f43
More review feedback.
carljm May 20, 2018
567e819
More review feedback.
carljm May 22, 2018
f7876d0
Minor review comments.
carljm Jul 28, 2018
354a975
Allow __set_name__ to set cached attribute name.
carljm Jul 28, 2018
f006f68
Fix consistency of doc example.
carljm Jul 28, 2018
d6bed4b
Explicitly require calling __set_name__ exactly once on cached_property.
carljm Jul 29, 2018
b41380d
Refine error message.
carljm Jul 29, 2018
b504a20
Allow reuse of cached_property as long as name remains the same.
carljm Jul 30, 2018
977ece0
Merge branch 'master' into cached-property
carljm Aug 19, 2018
5bdeaab
Clearer error message when __dict__ is not mutable.
carljm Aug 19, 2018
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@carljm
carljm committed Jul 28, 2018
commit 72259cda1b084cd6f3f6b1a63cc795602385f646
24 changes: 15 additions & 9 deletions Lib/functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -874,26 +874,32 @@ def __isabstractmethod__(self):
### cached_property() - computed once per instance, cached as attribute
################################################################################

_NOT_FOUND = object()


class cached_property:
def __init__(self, func):
self.func = func
self.__doc__ = func.__doc__
self.lock = RLock()

def __get__(self, instance, cls=None):
if instance is None:
def __get__(self, obj, objtype=None):
if obj is None:
return self
attrname = self.func.__name__
try:
cache = instance.__dict__
cache = obj.__dict__
except AttributeError: # objects with __slots__ have no __dict__

@ncoghlan ncoghlan Aug 4, 2018

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Tweak the comment here along similar lines to the note in the docs

msg = (
f"No '__dict__' attribute on {type(instance).__name__!r} "
f"No '__dict__' attribute on {type(obj).__name__!r} "
f"instance to cache {attrname!r} property."
)
raise TypeError(msg) from None
with self.lock:
# check if another thread filled cache while we awaited lock
if attrname not in cache:
cache[attrname] = self.func(instance)
return cache[attrname]
val = cache.get(attrname, _NOT_FOUND)
if val is _NOT_FOUND:
with self.lock:
# check if another thread filled cache while we awaited lock
val = cache.get(attrname, _NOT_FOUND)
if val is _NOT_FOUND:
val = cache[attrname] = self.func(obj)
return val