diff options
Diffstat (limited to 'Lib/functools.py')
| -rw-r--r-- | Lib/functools.py | 23 |
1 files changed, 13 insertions, 10 deletions
diff --git a/Lib/functools.py b/Lib/functools.py index 4d5e2709007..8518450a8d4 100644 --- a/Lib/functools.py +++ b/Lib/functools.py @@ -957,9 +957,10 @@ class singledispatchmethod: ################################################################################ -### cached_property() - computed once per instance, cached as attribute +### cached_property() - property result cached as instance attribute ################################################################################ +_NOT_FOUND = object() class cached_property: def __init__(self, func): @@ -990,15 +991,17 @@ class cached_property: f"instance to cache {self.attrname!r} property." ) raise TypeError(msg) from None - 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 + 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 __class_getitem__ = classmethod(GenericAlias) |