bpo-46066: Deprecate kwargs syntax for TypedDict definitions#31126

97littleleaf11 · 2022-02-04T07:55:57Z

https://bugs.python.org/issue46066

AlexWaygood · 2022-02-04T12:26:43Z

Surely this is a breaking change — even if type-checkers only understand the literal-dict assignment-based syntax, I'm not sure we can change the runtime behaviour like this without a deprecation period.

97littleleaf11 · 2022-02-04T14:09:07Z

Yeah, it changes the typing module. However I seldom see this syntax in real-world projects since we already have class based one.

97littleleaf11 · 2022-02-04T14:13:49Z

I am not really familiar with the cpython developing period. It's not a big deal since neither mypy nor other widely-used type checkers implement this feature and I barely see this syntax in real world projects.

AlexWaygood · 2022-02-04T14:14:23Z

Yeah, it changes the typing module. However I seldom see this syntax in real-world projects since we already have class based one.

I appreciate that — but given that this is a change to the stdlib, I think the standard deprecation policy probably still applies :)

97littleleaf11 · 2022-02-04T14:16:12Z

I think the standard deprecation policy probably still applies :)

Thanks for pointing out!

AlexWaygood · 2022-02-04T14:20:53Z

For now, I think I would:

Change the docs to state that this is deprecated in 3.11, will be removed in 3.13, and probably won't be understood by type checkers like mypy.
Change the runtime behaviour to emit a warning if a user tries to construct a TypedDict with the kwargs-based syntax.

Here's an example of a previous PR deprecating features, that you could look to as an example: #23064

Lib/typing.py

Doc/library/typing.rst

Lib/test/test_typing.py

Lib/typing.py

Misc/NEWS.d/next/Library/2022-02-08-16-42-20.bpo-46066.m32Hl0.rst

Co-authored-by: AlexWaygood <Alex.Waygood@Gmail.com>

AlexWaygood · 2022-02-08T15:55:17Z

Misc/ACKS

 Ka-Ping Yee
 Chi Hsuan Yen
 Jason Yeo
+Jingchen Ye


It feels absurd to bring this up (sorry!!), but: I think "Jingchen Ye" should go before "Ka-Ping Yee", if we're keeping this list alphabetised.

AlexWaygood · 2022-02-08T16:19:26Z

Also, it looks like there's some trailing whitespace in some of the documentation changes you've made, which is making the documentation-related tests fail -- could you possibly fix those issues?

97littleleaf11 · 2022-02-08T16:29:37Z

@AlexWaygood Thanks for your reviews! btw, it seems that CI reports wrong line number about the trailing whitespace.

AlexWaygood · 2022-02-08T16:33:44Z

@AlexWaygood Thanks for your reviews!

No worries, it's a good PR!

btw, it seems that CI reports wrong line number about the trailing whitespace.

Huh — no idea what might be causing that :)

AlexWaygood

LGTM

AlexWaygood · 2022-02-09T12:41:42Z

As this is a deprecation of an existing feature, I think it probably warrants a mention in "What's New in Python 3.11". I think @JelleZijlstra is planning on doing a PR for that document mentioning a bunch of recent changes to typing, though, so perhaps he'll be kind enough to include a mention of this as well :)

AlexWaygood · 2022-02-10T15:00:57Z

@gvanrossum, could we possibly get the full test suite run on this PR, please? :)

gvanrossum

I can't stand "firstly" and "secondly" for some reason. :-(

97littleleaf11 · 2022-02-12T16:29:45Z

I can't stand "firstly" and "secondly" for some reason. :-(

How about "The first one" and "The other one"?

arhadthedev · 2022-02-12T16:41:47Z

How about "The first one" and "The other one"?

Probably, a bullet list will be better. Like this:

[...] syntactic forms:
using a literal dict as the second argument:
Point2D = TypedDict('Point2D',{'x': int, 'y': int, 'label': str}) 
using keyword arguments:
Point2D = TypedDict('Point2D', x=int, y=int, label=str) 

JelleZijlstra

Here's a concrete wording suggestion that avoids "Firstly" and "Secondly"

JelleZijlstra · 2022-02-12T17:15:20Z

Doc/library/typing.rst

 support :pep:`526`, ``TypedDict`` supports two additional equivalent
- syntactic forms::
+ syntactic forms. Firstly, using a literal :class:`dict` as the
+ second argument::


I'd suggest just writing "a TypedDict may be created using a functional form". This parallels https://docs.python.org/3.10/library/enum.html#functional-api

Thanks for this!

JelleZijlstra · 2022-02-12T17:15:42Z

Doc/library/typing.rst

- Point2D = TypedDict('Point2D', x=int, y=int, label=str)
 Point2D = TypedDict('Point2D',{'x': int, 'y': int, 'label': str})

+ Secondly, using keyword arguments::


Suggested change
Secondly, using keyword arguments::
Keyword arguments may also be used::

gvanrossum · 2022-02-12T17:20:03Z

I was just hoping to see “first“ and “second”. No “ly” needed, these are flat adverbs.

Misc/NEWS.d/next/Library/2022-02-08-16-42-20.bpo-46066.m32Hl0.rst

gvanrossum · 2022-02-14T16:46:10Z

In a few days Jelle can likely merge this himself. :-)

Doc/library/typing.rst

gvanrossum · 2022-02-17T05:06:43Z

Congrats Jelle!

AlexWaygood · 2022-02-17T09:15:16Z

And congrats @97littleleaf11 on your first CPython contribution!

Remove kwargs syntax for TypedDict
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Add deprecation flag and warning
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Co-authored-by: AlexWaygood <Alex.Waygood@Gmail.com>

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97littleleaf11 changed the title ~~bpo-46066: Remove kwargs syntax for TypedDict definition~~bpo-46066: Deprecate kwargs syntax for TypedDict definitionsFeb 8, 2022

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JelleZijlstra mentioned this pull request Apr 13, 2022
Add typing to 3.11 What's New #91491
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97littleleaf11mannequin mentioned this pull request Dec 22, 2022
Deprecate keyword args syntax for TypedDict definition #90224
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	Secondly, using keyword arguments::
	Keyword arguments may also be used::

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bpo-46066: Deprecate kwargs syntax for TypedDict definitions#31126

bpo-46066: Deprecate kwargs syntax for TypedDict definitions #31126

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