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Add __override__ attribute to @override (PEP 698) #86

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Merged
JelleZijlstra merged 1 commit into from
Oct 20, 2022
Merged

Add __override__ attribute to @override (PEP 698) #86

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30 changes: 26 additions & 4 deletions src/test_typing_extensions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -164,16 +164,38 @@ def test_exception(self):
class OverrideTests(BaseTestCase):
def test_override(self):
class Base:
def foo(self): ...
def normal_method(self): ...
@staticmethod
def static_method_good_order(): ...
@staticmethod
def static_method_bad_order(): ...
@staticmethod
def decorator_with_slots(): ...

class Derived(Base):
@override
def foo(self):
def normal_method(self):
return 42

@staticmethod
@override
def static_method_good_order():
return 42

@override
@staticmethod
def static_method_bad_order():
return 42


self.assertIsSubclass(Derived, Base)
self.assertEqual(Derived().foo(), 42)
self.assertEqual(dir(Base.foo), dir(Derived.foo))
instance = Derived()
self.assertEqual(instance.normal_method(), 42)
self.assertIs(True, instance.normal_method.__override__)
self.assertEqual(Derived.static_method_good_order(), 42)
self.assertIs(True, Derived.static_method_good_order.__override__)
self.assertEqual(Derived.static_method_bad_order(), 42)
self.assertIs(False, hasattr(Derived.static_method_bad_order, "__override__"))


class AnyTests(BaseTestCase):
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11 changes: 11 additions & 0 deletions src/typing_extensions.py
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Expand Up @@ -2102,9 +2102,20 @@ def method(self) -> None:
This helps prevent bugs that may occur when a base class is changed
without an equivalent change to a child class.

There is no runtime checking of these properties. The decorator
sets the ``__override__`` attribute to ``True`` on the decorated object
to allow runtime introspection.

See PEP 698 for details.

"""
try:
__arg.__override__ = True
except (AttributeError, TypeError):
# Skip the attribute silently if it is not writable.
# AttributeError happens if the object has __slots__ or a
# read-only property, TypeError if it's a builtin class.
pass
return __arg


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