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pythongh-99535: Add test for inheritance of annotations and update do…
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…cumentation (pythonGH-99990)

(cherry picked from commit f5b7b19)

Co-authored-by: MonadChains <monadchains@gmail.com>
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MonadChains authored and miss-islington committed Dec 24, 2022
1 parent a7eee89 commit d6cac8e
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6 changes: 6 additions & 0 deletions Doc/howto/annotations.rst
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Expand Up @@ -57,6 +57,12 @@ Accessing The Annotations Dict Of An Object In Python 3.10 And Newer
newer is to call :func:`getattr` with three arguments,
for example ``getattr(o, '__annotations__', None)``.

Before Python 3.10, accessing ``__annotations__`` on a class that
defines no annotations but that has a parent class with
annotations would return the parent's ``__annotations__``.
In Python 3.10 and newer, the child class's annotations
will be an empty dict instead.


Accessing The Annotations Dict Of An Object In Python 3.9 And Older
===================================================================
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4 changes: 4 additions & 0 deletions Doc/library/typing.rst
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Expand Up @@ -2767,6 +2767,10 @@ Introspection helpers
.. versionchanged:: 3.9
Added ``include_extras`` parameter as part of :pep:`593`.

.. versionchanged:: 3.10
Calling ``get_type_hints()`` on a class no longer returns the annotations
of its base classes.

.. versionchanged:: 3.11
Previously, ``Optional[t]`` was added for function and method annotations
if a default value equal to ``None`` was set.
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22 changes: 22 additions & 0 deletions Lib/test/test_grammar.py
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Expand Up @@ -415,6 +415,28 @@ class Cbad2(C):
x: int
x.y: list = []

def test_annotations_inheritance(self):
# Check that annotations are not inherited by derived classes
class A:
attr: int
class B(A):
pass
class C(A):
attr: str
class D:
attr2: int
class E(A, D):
pass
class F(C, A):
pass
self.assertEqual(A.__annotations__, {"attr": int})
self.assertEqual(B.__annotations__, {})
self.assertEqual(C.__annotations__, {"attr" : str})
self.assertEqual(D.__annotations__, {"attr2" : int})
self.assertEqual(E.__annotations__, {})
self.assertEqual(F.__annotations__, {})


def test_var_annot_metaclass_semantics(self):
class CMeta(type):
@classmethod
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