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gh-99535: Add test for inheritance of annotations and update documentation #99990

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Dec 24, 2022
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gh-99535: Add test for inheritance of annotations and update documentation #99990

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0787052
Add test for inheritance of annotations and update documentation
MonadChains Dec 4, 2022
f5c7cee
Add multiple inheritance case to test
MonadChains Dec 4, 2022
671a262
Add note to get_type_hints
MonadChains Dec 6, 2022
24a118e
Add additional test
MonadChains Dec 7, 2022
67a0175
Rework annotations.rst addition
MonadChains Dec 18, 2022
ad64aab
Improve get_type_hints entry
MonadChains Dec 24, 2022
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6 changes: 6 additions & 0 deletions Doc/howto/annotations.rst
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Original file line number Diff line number Diff line change
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.
Comment on lines +60 to +64
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As mentioned in #99535 (comment), there is one edge case where this isn't true: TypedDicts still inherit a parent class's __annotations__, even in Python 3.10. I'm not sure whether it's important to mention that or not -- @hauntsaninja, do you have any thoughts on that?

Python 3.10.9 (tags/v3.10.9:1dd9be6, Dec  6 2022, 20:01:21) [MSC v.1934 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing import TypedDict
>>> class Foo(TypedDict):
...     x: int
...
>>> class Bar(Foo): ...
...
>>> Bar.__annotations__
{'x': <class 'int'>}

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I think it's fine not to mention over here:

  1. The special case is more that TypedDicts don't have a runtime subclassing relationship, rather than anything to do with __annotations__. In other words, if you know how TypedDict subclassing works at runtime (which is presumably documented somewhere), you can reasonable expect this __annotations__ behaviour. So adding more words here might be confusing; the statement about the language remains true
  2. My understanding of "HOWTO"s is that they're allowed to skip some of the gross details



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 @@ -2773,6 +2773,10 @@ 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):
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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})
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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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