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typing.get_args(Callable) fails #84578

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typing.get_args(Callable) fails#84578
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3.8 (EOL)end of life3.9 (EOL)end of lifestdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@serhiy-storchaka
serhiy-storchaka
opened on Apr 26, 2020
BPO 40398
Nosy @gvanrossum, @serhiy-storchaka, @ilevkivskyi
PRs
  • bpo-40398: Fix typing.get_args() for special generic aliases. #19720
  • [3.8] bpo-40398: Fix typing.get_args() for special generic aliases. (GH-19720) #19857
    		•

    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 2020-05-02.08:08:24.496>
created_at = <Date 2020-04-26.16:46:07.424>
labels = ['3.8', 'type-bug', 'library', '3.9']
title = 'typing.get_args(Callable) fails'
updated_at = <Date 2020-05-02.08:08:24.495>
user = 'https://github.com/serhiy-storchaka'

    bugs.python.org fields:

    activity = <Date 2020-05-02.08:08:24.495>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-05-02.08:08:24.496>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2020-04-26.16:46:07.424>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 40398
keywords = ['patch']
message_count = 10.0
messages = ['367313', '367322', '367327', '367328', '367329', '367331', '367405', '367898', '367919', '367920']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'levkivskyi']
pr_nums = ['19720', '19857']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40398'
versions = ['Python 3.8', 'Python 3.9']

    Activity

    1. serhiy-storchaka commented on Apr 26, 2020

      @serhiy-storchaka
      serhiy-storchaka
      on Apr 26, 2020
      MemberAuthor
      >>> from typing import *
>>> get_args(Callable)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/typing.py", line 1412, in get_args
    if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
IndexError: tuple index out of range

      What is the correct behavior?

    2. serhiy-storchaka
      added
      3.8 (EOL)end of life
      3.9 (EOL)end of life
      stdlibStandard Library Python modules in the Lib/ directory
      type-bugAn unexpected behavior, bug, or error
      on Apr 26, 2020

    3. gvanrossum commented on Apr 26, 2020

      @gvanrossum
      gvanrossum
      on Apr 26, 2020
      Member

      Maybe it could return (Ellipsis, Any) in that case. The most general form of Callable is Callable[..., Any] and that's that get_args() returns for that.

    4. ilevkivskyi commented on Apr 26, 2020

      @ilevkivskyi
      ilevkivskyi
      on Apr 26, 2020
      Member

      I think it should return empty tuple: First, for consistency with other things like get_args(Tuple) == () and get_args(List) == (). Second, although Callable is equivalent to Callable[..., Any] in the static world, authors of some runtime checkers might want to distinguish whether a user wrote one or another.

    5. gvanrossum commented on Apr 26, 2020

      @gvanrossum
      gvanrossum
      on Apr 26, 2020
      Member

      Agreed, that's better!

    6. serhiy-storchaka commented on Apr 26, 2020

      @serhiy-storchaka
      serhiy-storchaka
      on Apr 26, 2020
      MemberAuthor

      get_args(List) == (T,)

    7. ilevkivskyi commented on Apr 26, 2020

      @ilevkivskyi
      ilevkivskyi
      on Apr 26, 2020
      Member

      Oh my, this looks like another bug. I don't have Python 3.8 at hand so just tried typing_inspect on Python 3.6. I think this may be caused by the "double use" of _GenericAlias for which you opened your WIP PR.

    8. serhiy-storchaka commented on Apr 27, 2020

      @serhiy-storchaka
      serhiy-storchaka
      on Apr 27, 2020
      MemberAuthor

      New changeset 6292be7 by Serhiy Storchaka in branch 'master':
      bpo-40398: Fix typing.get_args() for special generic aliases. (GH-19720)
      6292be7

    9. terryjreedy
      changed the title [-]get_args(Callable) fails[/-] [+]typing.get_args(Callable) fails[/+] on May 1, 2020
    10. terryjreedy
      changed the title [-]get_args(Callable) fails[/-] [+]typing.get_args(Callable) fails[/+] on May 1, 2020

    11. gvanrossum commented on May 1, 2020

      @gvanrossum
      gvanrossum
      on May 1, 2020
      Member

      @serhiy is this fixed by PR 19720?

    12. serhiy-storchaka commented on May 2, 2020

      @serhiy-storchaka
      serhiy-storchaka
      on May 2, 2020
      MemberAuthor

      Yes, I have not closed this issue yet because it required a manual backporting to 3.8.

    13. serhiy-storchaka commented on May 2, 2020

      @serhiy-storchaka
      serhiy-storchaka
      on May 2, 2020
      MemberAuthor

      New changeset a629d4c by Serhiy Storchaka in branch '3.8':
      [3.8] bpo-40398: Fix typing.get_args() for special generic aliases. (GH-19720) (GH-19857)
      a629d4c

    14. serhiy-storchaka
      closed this as completedon May 2, 2020
    15. serhiy-storchaka
      closed this as completedon May 2, 2020
    16. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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