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bpo-34995: Maintain func.__isabstractmethod__ in functools.cached_property #9904

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mwilbz wants to merge 6 commits into from
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bpo-34995: Maintain func.__isabstractmethod__ in functools.cached_property #9904

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da3ec33
bpo-34995: Maintain func.__isabstractmethod__ in functools.cached_pro…
Oct 15, 2018
bfdc249
Add news entry
Oct 15, 2018
16c0372
Only set __isabstractmethod__ if wrapapped func sets it
Oct 25, 2018
db8dcd7
Check for __isabstractmethod__ with try/except
Oct 25, 2018
1c91dd2
Add negative test case for abstract cached_property
Oct 25, 2018
511c14f
Avoid long lines
Oct 26, 2018
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4 changes: 4 additions & 0 deletions Lib/functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -882,6 +882,10 @@ def __init__(self, func):
self.func = func
self.attrname = None
self.__doc__ = func.__doc__
try:
self.__isabstractmethod__ = func.__isabstractmethod__
except AttributeError:
pass
self.lock = RLock()

def __set_name__(self, owner, name):
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22 changes: 22 additions & 0 deletions Lib/test/test_functools.py
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Expand Up @@ -2478,6 +2478,28 @@ def test_access_from_class(self):
def test_doc(self):
self.assertEqual(CachedCostItem.cost.__doc__, "The cost of the item.")

def test_isabstractmethod_copied(self):
class AbstractExpensiveCalculator(abc.ABC):
@functools.cached_property
@abc.abstractmethod
def calculate(self):
pass

method = AbstractExpensiveCalculator.calculate
self.assertTrue(method.__isabstractmethod__)
with self.assertRaises(TypeError):
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@vstinner vstinner Oct 25, 2018

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Would it be possible to (also) directly check the isabstractmethod attribute?

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@mwilbz mwilbz Oct 25, 2018

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Good suggestion, added an assertion for that

AbstractExpensiveCalculator()

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@vstinner vstinner Oct 25, 2018

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Can you add a test on a method which doesn't have the __isabstractmethod__ attribute? I expect such test:

self.assertFalse(hasattr(AbstractExpensiveCalculator.calculate, '__isabstractmethod__'))

def test_missing_isabstractmethod_not_copied(self):
class ConcreteExpensiveCalculator(abc.ABC):
@functools.cached_property
def calculate(self):
return 42

method = ConcreteExpensiveCalculator.calculate
self.assertFalse(getattr(method, '__isabstractmethod__', False))
ConcreteExpensiveCalculator()


if __name__ == '__main__':
unittest.main()
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-10-15-23-56-39.bpo-34995.kNA9ge.rst
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@@ -0,0 +1 @@
:func:`functools.cached_property` now also copies the wrapped method's ``__isabstractmethod__`` attribute.