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

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merged 11 commits into from Feb 17, 2022

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97littleleaf11
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@97littleleaf11 97littleleaf11 commented Feb 4, 2022

@the-knights-who-say-ni

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@AlexWaygood
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AlexWaygood commented Feb 4, 2022

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.

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97littleleaf11 commented Feb 4, 2022

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

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97littleleaf11 commented Feb 4, 2022

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.

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AlexWaygood commented Feb 4, 2022

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 :)

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97littleleaf11 commented Feb 4, 2022

I think the standard deprecation policy probably still applies :)

Thanks for pointing out!

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AlexWaygood commented Feb 4, 2022

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

@97littleleaf11 97littleleaf11 marked this pull request as ready for review Feb 7, 2022
@gvanrossum gvanrossum requested a review from JelleZijlstra Feb 7, 2022
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97littleleaf11 and others added 2 commits Feb 8, 2022
Co-authored-by: AlexWaygood <Alex.Waygood@Gmail.com>
@97littleleaf11 97littleleaf11 changed the title bpo-46066: Remove kwargs syntax for TypedDict definition bpo-46066: Deprecate kwargs syntax for TypedDict definitions Feb 8, 2022
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@@ -1976,6 +1976,7 @@ Masayuki Yamamoto
Ka-Ping Yee
Chi Hsuan Yen
Jason Yeo
Jingchen Ye
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@AlexWaygood AlexWaygood Feb 8, 2022

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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.

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AlexWaygood commented Feb 8, 2022

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?

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97littleleaf11 commented Feb 8, 2022

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

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AlexWaygood commented Feb 8, 2022

@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 :)

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@AlexWaygood AlexWaygood left a comment

LGTM

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AlexWaygood commented Feb 9, 2022

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 AlexWaygood requested a review from JelleZijlstra Feb 10, 2022
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AlexWaygood commented Feb 10, 2022

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

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@gvanrossum gvanrossum left a comment

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

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97littleleaf11 commented Feb 12, 2022

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

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

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arhadthedev commented Feb 12, 2022

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)
    

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@JelleZijlstra JelleZijlstra left a comment

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

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

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@97littleleaf11 97littleleaf11 Feb 13, 2022

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Thanks for this!

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

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

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gvanrossum commented Feb 12, 2022

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

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gvanrossum commented Feb 14, 2022

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

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@JelleZijlstra JelleZijlstra merged commit de6043e into python:main Feb 17, 2022
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gvanrossum commented Feb 17, 2022

Congrats Jelle!

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AlexWaygood commented Feb 17, 2022

And congrats @97littleleaf11 on your first CPython contribution!

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TypedDict alternative definition syntax with keyword args is confusing
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