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typing: allow Annotated in outermost scope #90649

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typing: allow Annotated in outermost scope#90649
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3.10 (EOL)end of life3.11only security fixes3.9 (EOL)end of lifestdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@GBeauregard
GBeauregard
mannequin
opened on Jan 23, 2022
BPO 46491
Nosy @gvanrossum, @JelleZijlstra, @asottile, @miss-islington, @Fidget-Spinner, @GBeauregard
PRs
  • bpo-46491: Allow Annotated on outside of Final/ClassVar #30864
  • [3.10] bpo-46491: Allow Annotated on outside of Final/ClassVar (GH-30864) #30873
  • [3.9] bpo-46491: Allow Annotated on outside of Final/ClassVar (GH-30864) #30874
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2022-01-25.14:40:07.659>
created_at = <Date 2022-01-23.19:03:20.373>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'typing: allow Annotated in outermost scope'
updated_at = <Date 2022-01-26.00:26:54.760>
user = 'https://github.com/GBeauregard'

    bugs.python.org fields:

    activity = <Date 2022-01-26.00:26:54.760>
actor = 'gvanrossum'
assignee = 'none'
closed = True
closed_date = <Date 2022-01-25.14:40:07.659>
closer = 'kj'
components = ['Library (Lib)']
creation = <Date 2022-01-23.19:03:20.373>
creator = 'GBeauregard'
dependencies = []
files = []
hgrepos = []
issue_num = 46491
keywords = ['patch']
message_count = 13.0
messages = ['411404', '411405', '411418', '411557', '411598', '411599', '411600', '411686', '411688', '411690', '411691', '411692', '411693']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'JelleZijlstra', 'Anthony Sottile', 'miss-islington', 'kj', 'GBeauregard']
pr_nums = ['30864', '30873', '30874']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46491'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

    Activity

    1. GBeauregard commented on Jan 23, 2022

      @GBeauregard
      GBeauregardmannequin
      on Jan 23, 2022
      MannequinAuthor

      Currently, typing.Annotated (PEP-593) cannot be used at runtime with typing.Final and typing.ClassVar with Annotated on the outside:

      from typing import Annotated, Final
# TypeError: typing.Final[int] is not valid as type argument
var: Annotated[Final[int], "foo"] = 4

      The only tenuously related mention of this I can find in a PEP is in PEP-593 (Annotated) which states "The first argument to Annotated must be a valid type".

      I believe the runtime behavior should be changed to allow any ordering for Annotated with ClassVar and Final. This was discussed in the typing-sig PEP-655 thread (TypedDict Required and NotRequired) where the current plan is to allow Required/NotRequired in any nesting order with Annotated while suggesting the ClassVar/Final ordering restriction be lifted: https://mail.python.org/archives/list/typing-sig@python.org/message/22CJ5TJGIJ563D6ZKB7R3VUZXTZQND5X/

      The argument for doing so is on the mailing list: https://mail.python.org/archives/list/typing-sig@python.org/message/MPMOIBX3XFXCD4ZNDC6AV4CLSI5LN544/

      To summarize: adopting an overly strict view of what constitutes a valid type for Annotated creates difficulties for people who use runtime introspection of Annotated annotations by requiring them to parse additional typing or field annotations (https://bugs.python.org/msg411067). This needlessly exacerbates tension between typing and non-typing uses of annotation space. In order to be a good citizen to other annotation users, the Annotated runtime ordering restriction should be lifted.

    2. GBeauregard
      added
      3.9 (EOL)end of life
      3.10 (EOL)end of life
      3.11only security fixes
      type-bugAn unexpected behavior, bug, or error
      on Jan 23, 2022

    3. JelleZijlstra commented on Jan 23, 2022

      @JelleZijlstra
      JelleZijlstra
      on Jan 23, 2022
      Member

      I support making this change. It looks like the simplest implementation is simply to remove the mention of ClassVar and Final in typing._type_check.

    4. JelleZijlstra
      added
      stdlibStandard Library Python modules in the Lib/ directory
      on Jan 23, 2022

    5. gvanrossum commented on Jan 23, 2022

      @gvanrossum
      gvanrossum
      on Jan 23, 2022
      Member

      +1--
      --Guido (mobile)

    6. miss-islington commented on Jan 25, 2022

      @miss-islington
      miss-islington
      on Jan 25, 2022
      Contributor

      New changeset e1abffc by Gregory Beauregard in branch 'main':
      bpo-46491: Allow Annotated on outside of Final/ClassVar (GH-30864)
      e1abffc

    7. miss-islington commented on Jan 25, 2022

      @miss-islington
      miss-islington
      on Jan 25, 2022
      Contributor

      New changeset 41e0aea by Miss Islington (bot) in branch '3.10':
      bpo-46491: Allow Annotated on outside of Final/ClassVar (GH-30864)
      41e0aea

    8. miss-islington commented on Jan 25, 2022

      @miss-islington
      miss-islington
      on Jan 25, 2022
      Contributor

      New changeset b0b8388 by Miss Islington (bot) in branch '3.9':
      bpo-46491: Allow Annotated on outside of Final/ClassVar (GH-30864)
      b0b8388

    9. Fidget-Spinner commented on Jan 25, 2022

      @Fidget-Spinner
      Fidget-Spinner
      on Jan 25, 2022
      Member

      Thanks Gregory for fixing this!

    10. Fidget-Spinner
      closed this as completedon Jan 25, 2022
    11. Fidget-Spinner
      closed this as completedon Jan 25, 2022

    12. asottile commented on Jan 25, 2022

      @asottile
      asottilemannequin
      on Jan 25, 2022
      Mannequin

      should this behaviour change be backported? it potentially creates an annoying edgecase where code seemingly works unless you use an older patch version

      since this isn't a bugfix I wouldn't expect this to land in 3.9 and 3.10

    13. gvanrossum commented on Jan 25, 2022

      @gvanrossum
      gvanrossum
      on Jan 25, 2022
      Member

      But it *is* a bugfix.

    14. asottile commented on Jan 25, 2022

      @asottile
      asottilemannequin
      on Jan 25, 2022
      Mannequin

      to me this is the same as the Union[Pattern] / Union[Match] "fixes" that landed in 3.5.3 -- and the pain caused by using that and having CI pass (because of modern 3.5.x) but having spurious bug reports from users stuck on 3.5.2

      or in 3.6.1 when NamedTuple was "fixed" to allow methods, again having CI pass with modern pythons but having frustrated users running 3.6.0

      I forsee the same class of problems here with Annotated where it works great in 3.10.3 and 3.9.11 but anyone stuck on 3.10.2 or 3.9.10 or older will be broken

    15. gvanrossum commented on Jan 26, 2022

      @gvanrossum
      gvanrossum
      on Jan 26, 2022
      Member

      Well that's *always* a problem right? If you take that to the extreme we wouldn't need bugfix releases. :-)

      Apart from some examples in the 3.5-3.6 timeframe, what makes you think that *this* fix *specifically* is going to make more people unhappy than it makes happy?

      When people complain that they wrote Annotated[ClassVar[int], ...] and are disappointed that it doesn't work in a certain old version, you can just tell them to use ClassVar[Annotated[int, ...]] which is in no way invalid or inferior and works in all versions that support Annotated.

    16. asottile commented on Jan 26, 2022

      @asottile
      asottilemannequin
      on Jan 26, 2022
      Mannequin

      3.7.2 has another example where OrderedDict was added to typing

      I don't have any personal investment in this particular change but I've had quite a few unhappy consumers of libraries due to instability in typing apis between patch versions in the past (heh and they're especially frustrated because they don't care about type checking and just want functional software)

      it's also difficult and/or not cost effective to add every patch version to a CI matrix to catch these sorts of problems

    17. gvanrossum commented on Jan 26, 2022

      @gvanrossum
      gvanrossum
      on Jan 26, 2022
      Member

      Yeah, there are no perfect solutions. Please let it go.

    18. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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