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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
Merged

bpo-21145: Add cached_property decorator in functools #6982

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1cda951
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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Allow reuse of cached_property as long as name remains the same.
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@carljm
carljm committed Jul 30, 2018
commit b504a20942cc7143958cf6afaabae4b888b393d4
6 changes: 3 additions & 3 deletions Lib/functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -887,10 +887,10 @@ def __init__(self, func):
def __set_name__(self, owner, name):
if self.attrname is None:
self.attrname = name
else:
elif name != self.attrname:
raise TypeError(
"Cannot assign the same cached_property to two names "
f"({self.attrname!r} and {name!r}) on the same class."
"Cannot assign the same cached_property to two different names "
f"({self.attrname!r} and {name!r})."
)

def __get__(self, instance, owner):
Expand Down
27 changes: 25 additions & 2 deletions Lib/test/test_functools.py
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Expand Up @@ -2406,7 +2406,7 @@ def test_object_with_slots(self):
):
item.cost

def test_reuse(self):
def test_reuse_different_names(self):
"""Disallow this case because decorated function a would not be cached."""
with self.assertRaises(RuntimeError) as ctx:
class ReusedCachedProperty:
Expand All @@ -2418,9 +2418,32 @@ def a(self):

self.assertEqual(
str(ctx.exception.__context__),
str(TypeError("Cannot assign the same cached_property to two names ('a' and 'b') on the same class."))
str(TypeError("Cannot assign the same cached_property to two different names ('a' and 'b')."))
)

def test_reuse_same_name(self):
"""Reusing a cached_property on different classes under the same name is OK."""
counter = 0

@py_functools.cached_property
def _cp(_self):
nonlocal counter
counter += 1
return counter

class A:
cp = _cp

class B:
cp = _cp

a = A()
b = B()

self.assertEqual(a.cp, 1)
self.assertEqual(b.cp, 2)
self.assertEqual(a.cp, 1)

def test_set_name_not_called(self):
cp = py_functools.cached_property(lambda s: None)
class Foo:
Expand Down