Description

johnslavik

opened on Feb 26, 2026

Issue body actions

Feature or enhancement

Proposal:

Consider a specialized syntax error for these cases:

# Unary addition isn't allowed but we parse it for better error recovery.
match subject:
    case +1:
        pass
    case 1 | +2 | -3:
        pass
    case [1, +2, -3]:
        pass
    case Foo(x=+1, y=-2):
        pass
    case {True: +1, False: -2}:
        pass

This was taken from https://github.com/astral-sh/ruff/blob/6ff4da454c448f01eb0b71728f3941870c811bfc/crates/ruff_python_parser/resources/invalid/statements/match/unary_add_usage.py. 2+ years in Ruff's parser.

Current vs proposed:

❯ ./python.exe t.py
  File "/Users/bartosz.slawecki/Python/cpython/t.py", line 2
    case +1:
         ^
-SyntaxError: invalid syntax
+SyntaxError: cannot use unary addition in a literal pattern

The code doesn't look incorrect syntactically, which is why I think it's a good idea to add a more specific message (although it is not extremely unclear as-is assuming a pointer ^ is shown).

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-145239: Specialize match syntax error for unary addition in pattern #145658
• gh-145239: Accept unary plus literal pattern #148566
• gh-145239: Colorize case + in the REPL #150979

Activity

1. johnslavik

   self-assigned this

   on Feb 26, 2026
2. johnslavik

   added

   type-featureA feature request or enhancementA feature request or enhancement

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   topic-parser

   on Feb 26, 2026
3. johnslavik

   removed their assignment

   on Feb 26, 2026
4. johnslavik commented on Feb 26, 2026

   

   johnslavik

   on Feb 26, 2026

   MemberAuthor

   More actions

   cc @sobolevn @Eclips4 @pablogsal
5. pablogsal commented on Feb 26, 2026

   

   pablogsal

   on Feb 26, 2026

   Member

   More actions

   CC @brandtbucher
6. mvanhorn

   added a commit that references this issue on Mar 9, 2026

   pythongh-145239: Specialize match syntax error for unary addition in …

   3b7072e
7. mvanhorn commented on Mar 9, 2026

   

   mvanhorn

   on Mar 9, 2026

   Contributor

   More actions

   I've submitted a PR for this: #145658

   The approach adds an invalid_literal_pattern rule to the PEG grammar that catches '+' NUMBER and raises the error: "cannot use unary '+' in a literal pattern". This covers all the pattern contexts mentioned in the issue (top-level, alternatives, sequences, class patterns, and mapping patterns).

   This contribution was developed with AI assistance (Claude Code).
8. encukou commented on Mar 10, 2026

   

   encukou

   on Mar 10, 2026

   Member

   More actions

   Should we accept + instead?
   ast.literal_eval allows it. Also, 3e+1 is a valid spelling for 3e1 (using a different mechanism of course).

   Personally, I'd love to be able to write:

   match direction:
       case 0, +1: go_up()
       case 0, -1: go_down()
       case -1, 0: go_left()
       case +1, 0: go_right()

   Reacted by Bartosz Sławecki and Kirill Podoprigora
9. johnslavik commented on Mar 10, 2026

   

   johnslavik

   on Mar 10, 2026

   MemberAuthor

   More actions

   @encukou yeah, +1 (no pun intended). I'd love to see it supported and actually started implementing that locally. Do you think I should open a DPO? Is it minor enough to not need a PEP?
10. encukou commented on Mar 10, 2026

    

    encukou

    on Mar 10, 2026

    Member

    More actions

    I'd wait a day or two in case a parser expert wants to veto the idea here :)

    Reacted by Bartosz Sławecki
11. johnslavik commented on Mar 10, 2026

    

    johnslavik

    on Mar 10, 2026

    MemberAuthor

    More actions

    cc @pablogsal
12. khalidsaidi commented on Mar 25, 2026

    

    khalidsaidi

    on Mar 25, 2026 · Hidden as spam

    show commentMore actions
13. johnslavik

    self-assigned this

    on Mar 25, 2026
14. johnslavik

    added 3 commits that reference this issue on Apr 13, 2026

    pythongh-145239: Accept unary plus in match literal patterns

    004646e

    pythongh-145239: Add tests for unary plus in match literal patterns

    b30bc97

    pythongh-145239: Add NEWS entry

    5bb1a93
15. Eclips4

    added a commit that references this issue on Apr 23, 2026

    gh-145239: Accept unary plus literal pattern (#148566)

    448d7b9
16. johnslavik

    closed this as completedon Apr 24, 2026
17. ljfp

    added a commit that references this issue on Apr 25, 2026

    pythongh-145239: Accept unary plus literal pattern (python#148566)

    c1a69cf
18. Eclips4

    added a commit that references this issue on Jun 10, 2026

    gh-145239: Colorize `case +` in the REPL (#150979)

    ff64d8d
19. philthompson10

    added a commit that references this issue on Jun 17, 2026

    pythongh-145239: Colorize `case +` in the REPL (python#150979)

    513e89c
20. stealth-rklopper

    added a commit that references this issue on Oct 19, 2026

    feat: accept a plus sign in literal patterns

    1d21366

Issue actions