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Equality of typing.Literal depends on the order of arguments #86511

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Equality of typing.Literal depends on the order of arguments#86511
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3.10 (EOL)end of life3.8 (EOL)end of life3.9 (EOL)end of lifetype-bugAn unexpected behavior, bug, or error

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@Dominik1123
Dominik1123
mannequin
opened on Nov 13, 2020
BPO 42345
Nosy @gvanrossum, @ilevkivskyi, @miss-islington, @uriyyo, @Dominik1123, @Fidget-Spinner
PRs
  • bpo-42345: Fix three issues with typing.Literal parameters #23294
  • [3.9] bpo-42345: Fix three issues with typing.Literal parameters (GH-23294) #23335
  • bpo-42345: Fix hash implementation of typing.Literal #23383
  • bpo-42345: Add whatsnew for typing.Literal in 3.10 #23385
  • bpo-42345: Add whatsnew and versionchanged for typing.Literal in 3.9 #23386
  • [3.9] bpo-42345: Fix hash implementation of typing.Literal (GH-23383) #23408
  • [3.9] bpo-42345: Add whatsnew and versionchanged for typing.Literal in 3.9 (GH-23386) #23411
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    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 2020-11-20.17:11:24.442>
created_at = <Date 2020-11-13.14:11:55.639>
labels = ['type-bug', '3.8', '3.9', '3.10']
title = 'Equality of typing.Literal depends on the order of arguments'
updated_at = <Date 2021-10-13.10:26:49.678>
user = 'https://github.com/Dominik1123'

    bugs.python.org fields:

    activity = <Date 2021-10-13.10:26:49.678>
actor = 'kj'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-20.17:11:24.442>
closer = 'gvanrossum'
components = []
creation = <Date 2020-11-13.14:11:55.639>
creator = 'Dominik V.'
dependencies = []
files = []
hgrepos = []
issue_num = 42345
keywords = ['patch']
message_count = 17.0
messages = ['380888', '380904', '381018', '381050', '381204', '381247', '381249', '381380', '381388', '381439', '381441', '381445', '381446', '381448', '381469', '403752', '403818']
nosy_count = 7.0
nosy_names = ['gvanrossum', 'alick', 'levkivskyi', 'miss-islington', 'uriyyo', 'Dominik V.', 'kj']
pr_nums = ['23294', '23335', '23383', '23385', '23386', '23408', '23411']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42345'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

    Activity

    1. Dominik1123 commented on Nov 13, 2020

      @Dominik1123
      Dominik1123mannequin
      on Nov 13, 2020
      MannequinAuthor

      PEP-586 specifies that

      Literal[v1, v2, v3]

      is equivalent to

      Union[Literal[v1], Literal[v2], Literal[v3]]

      Since the equality of Unions doesn't take into account the order of arguments, Literals parametrized with multiple arguments should not be order dependent either. However they seem to:

          >>> Literal[1, 2] == Literal[2, 1]
    False

      Compare with the equivalent form:

          >>> Union[Literal[1], Literal[2]] == Union[Literal[2], Literal[1]]
    True

      In addition to that, the PEP specifies that nested Literals should be equivalent to the flattened version (https://www.python.org/dev/peps/pep-0586/#legal-parameters-for-literal-at-type-check-time). This section is titled "Legal parameters for Literal at type check time" but since the PEP doesn't specify runtime behavior differently, I think it makes sense to assume it is the same. It seems to be different though:

          >>> Literal[Literal[1, 2], 3]
    typing.Literal[typing.Literal[1, 2], 3]
    >>> Literal[Literal[1, 2], 3] == Literal[1, 2, 3]
    False

      Also the flattening follows from the above definition Literal[v1, v2, v3] == Union[Literal[v1], Literal[v2], Literal[v3]] and the fact that Unions are flattened.

    2. Dominik1123
      added
      3.9 (EOL)end of life
      type-bugAn unexpected behavior, bug, or error
      on Nov 13, 2020

    3. gvanrossum commented on Nov 13, 2020

      @gvanrossum
      gvanrossum
      on Nov 13, 2020
      Member

      Probably the implementation focused on static typing, not runtime checking.

      Can you come up with a PR for a fix?

    4. gvanrossum
      added
      3.8 (EOL)end of life
      3.10 (EOL)end of life
      on Nov 13, 2020

    5. Fidget-Spinner commented on Nov 15, 2020

      @Fidget-Spinner
      Fidget-Spinner
      on Nov 15, 2020
      Member

      @guido and @ivan,

      Should Literals de-duplicate values in its __args__ similar to Union? PEP-586 states that:

      Literal[v1, v2, v3] is equivalent to Union[Literal[v1], Literal[v2], Literal[v3]]

      Naturally, a Union de-duplicates values, so I was wondering if Literal should follow.

    6. gvanrossum commented on Nov 16, 2020

      @gvanrossum
      gvanrossum
      on Nov 16, 2020
      Member

      Yeah, I think it makes sense to de-dupe args for Literal.

    7. miss-islington commented on Nov 17, 2020

      @miss-islington
      miss-islington
      on Nov 17, 2020
      Contributor

      New changeset f03d318 by Yurii Karabas in branch 'master':
      bpo-42345: Fix three issues with typing.Literal parameters (GH-23294)
      f03d318

    8. miss-islington commented on Nov 17, 2020

      @miss-islington
      miss-islington
      on Nov 17, 2020
      Contributor

      New changeset ac472b3 by Yurii Karabas in branch '3.9':
      [3.9] bpo-42345: Fix three issues with typing.Literal parameters (GH-23294) (GH-23335)
      ac472b3

    9. gvanrossum commented on Nov 17, 2020

      @gvanrossum
      gvanrossum
      on Nov 17, 2020
      Member

      I recommend adding a whatsnew entry too. You can just add it to this issue. Interestingly you’ll probably need two separate ones, for 3.9 and 3.10. That would become two separate PRs for master, the 3.9 one to be backported.

    10. 1 remaining item

    11. gvanrossum
      closed this as completedon Nov 17, 2020

    12. gvanrossum commented on Nov 18, 2020

      @gvanrossum
      gvanrossum
      on Nov 18, 2020
      Member

      We need to fix this to make __hash__ match __eq__.

    13. gvanrossum
      reopened this on Nov 18, 2020
    14. gvanrossum
      reopened this on Nov 18, 2020

    15. gvanrossum commented on Nov 19, 2020

      @gvanrossum
      gvanrossum
      on Nov 19, 2020
      Member

      New changeset 4687338 by kj in branch 'master':
      bpo-42345: Add whatsnew for typing.Literal in 3.10 (GH-23385)
      4687338

    16. miss-islington commented on Nov 19, 2020

      @miss-islington
      miss-islington
      on Nov 19, 2020
      Contributor

      New changeset 1b54077 by Yurii Karabas in branch 'master':
      bpo-42345: Fix hash implementation of typing.Literal (GH-23383)
      1b54077

    17. miss-islington commented on Nov 19, 2020

      @miss-islington
      miss-islington
      on Nov 19, 2020
      Contributor

      New changeset 2acd9d0 by Miss Islington (bot) in branch '3.9':
      bpo-42345: Fix hash implementation of typing.Literal (GH-23383)
      2acd9d0

    18. miss-islington commented on Nov 19, 2020

      @miss-islington
      miss-islington
      on Nov 19, 2020
      Contributor

      New changeset e1dc0db by kj in branch 'master':
      bpo-42345: Add whatsnew and versionchanged for typing.Literal in 3.9 (GH-23386)
      e1dc0db

    19. gvanrossum commented on Nov 19, 2020

      @gvanrossum
      gvanrossum
      on Nov 19, 2020
      Member

      Thanks everyone! Can I close this now?

    20. miss-islington commented on Nov 19, 2020

      @miss-islington
      miss-islington
      on Nov 19, 2020
      Contributor

      New changeset 1051ca4 by Miss Islington (bot) in branch '3.9':
      bpo-42345: Add whatsnew and versionchanged for typing.Literal in 3.9 (GH-23386)
      1051ca4

    21. uriyyo commented on Nov 20, 2020

      @uriyyo
      uriyyo
      on Nov 20, 2020
      Member

      Looks like everything merged, we can close this issue

    22. gvanrossum
      closed this as completedon Nov 20, 2020

    23. alick commented on Oct 12, 2021

      @alick
      alickmannequin
      on Oct 12, 2021
      Mannequin

      Mainly to clarify, this is fixed in Python 3.9 and above, but won't be fixed in Python 3.8, right?

      ~$ python3.8
Python 3.8.11 (default, Jul 24 2021, 13:24:12)
[Clang 12.0.5 (clang-1205.0.22.11)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
Could not open PYTHONSTARTUP
FileNotFoundError: [Errno 2] No such file or directory: '/Users/taoz/.pythonstartup'
>>> from typing import Literal
>>> Literal[1,2]==Literal[2,1]
False
>>>

    24. Fidget-Spinner commented on Oct 13, 2021

      @Fidget-Spinner
      Fidget-Spinner
      on Oct 13, 2021
      Member

      @alick yes. To be specific, 3.9.1 and above. 3.9.0 still has the old
      behavior.

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