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ncoghlan opened this issue Sep 16, 2024 · 4 comments
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Document Annotated.__origin__ #124120

ncoghlan opened this issue Sep 16, 2024 · 4 comments
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docs Documentation in the Doc dir topic-typing

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@ncoghlan
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ncoghlan commented Sep 16, 2024 •
edited by bedevere-app bot
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The typing module docs cover using Annotated.__metadata__ to retrieve the annotations, but they do not currently cover the use of Annotated.__origin__ to retrieve the underlying type hint that is being annotated.

>>> from typing import Annotated
>>> Annotated[int, ""].__metadata__
('',)
>>> Annotated[int, ""].__origin__
<class 'int'>

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@ncoghlan ncoghlan added the docs Documentation in the Doc dir label Sep 16, 2024
@JelleZijlstra
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You should not use this directly, but use typing.get_origin instead. However, we could document this explicitly.

sobolevn added a commit to sobolevn/cpython that referenced this issue Sep 16, 2024
@sobolevn
pythongh-124120: Document use of get_origin to access Annotated o…
748a3c7 
…rigin
@bedevere-app bedevere-app bot mentioned this issue Sep 16, 2024
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@JelleZijlstra
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Actually, looking at the code some more this is not true. For some reason there is a special case where .__origin__ and get_origin() (as well as __args__ and get_args()) are not aligned for Annotated.

>>> a = Annotated[int, "x"]
>>> a.__origin__
<class 'int'>
>>> a.__args__
(<class 'int'>,)
>>> typing.get_origin(a)
<class 'typing.Annotated'>
>>> typing.get_args(a)
(<class 'int'>, 'x')

This aligns with the documentation, which promises that for X[Y, ...], get_origin() will return X. However, it is confusing that it does not also align with the __origin_ attribute.

Since __origin__ is otherwise undocumented, it's probably best to document it specifically for Annotated as @ncoghlan originally suggested.

@sobolevn
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I made this mistake in the first version of #124125

But, then I realized the same thing as in #124120 (comment)

Why? Because of these two lines:

cpython/Lib/typing.py

Lines 2507 to 2508 in 9aa1f60

if isinstance(tp, _AnnotatedAlias):
return Annotated

I think that it makes sense:

Get the unsubscripted version of a type.

So, Annotated is the unsubscripted version of a type. And any T wrapped by it is just the first type arg.

sobolevn added a commit that referenced this issue Sep 24, 2024
@sobolevn @brianschubert @AlexWaygood
gh-124120: Document Annotated.__origin__ (#124125)
faef3fa 
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Sep 24, 2024
@sobolevn @brianschubert
@AlexWaygood @miss-islington
pythongh-124120: Document Annotated.__origin__ (pythonGH-124125)
270c80f 
(cherry picked from commit faef3fa)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Sep 24, 2024
@sobolevn @brianschubert
@AlexWaygood @miss-islington
pythongh-124120: Document Annotated.__origin__ (pythonGH-124125)
bacb190 
(cherry picked from commit faef3fa)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
This was referenced Sep 24, 2024
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sobolevn added a commit that referenced this issue Sep 24, 2024
@miss-islington @sobolevn
@brianschubert @AlexWaygood
[3.12] gh-124120: Document Annotated.__origin__ (GH-124125) (#124417)
0c36c37 
gh-124120: Document `Annotated.__origin__` (GH-124125)
(cherry picked from commit faef3fa)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Yhg1s pushed a commit that referenced this issue Sep 24, 2024
@miss-islington @sobolevn
@brianschubert @AlexWaygood
[3.13] gh-124120: Document Annotated.__origin__ (GH-124125) (#124416)
8c0c344 
gh-124120: Document `Annotated.__origin__` (GH-124125)
(cherry picked from commit faef3fa)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
@ncoghlan
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Backports have been merged, so marking this as complete. Thanks, folks!

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