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

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Merged
JelleZijlstra merged 6 commits into from
Dec 24, 2022
Merged

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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Rework annotations.rst addition
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MonadChains committed Dec 18, 2022
commit 67a0175932952f1d39b39c73b3b9951a59fc15ae
8 changes: 5 additions & 3 deletions Doc/howto/annotations.rst
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Expand Up @@ -57,9 +57,11 @@ 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)``.

Starting from Python 3.10, accessing the annotations
of a class will not give anymore the ones of its base
classes.
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.
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@AlexWaygood AlexWaygood Jan 7, 2023

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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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@hauntsaninja hauntsaninja Jan 7, 2023

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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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