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GeezerVison is showing github.com — Disallow lone starred expressions at the *grammar* level · Issue #156058 · python/cpython

Disallow lone starred expressions at the *grammar* level #156058

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Disallow lone starred expressions at the *grammar* level#156058
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encukou
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interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)topic-parser

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@encukou
encukou
opened on Aug 19, 2026
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Statements like the following (where () can be any iterable -- or at the syntax level, any value):

  • *()
  • x = *()
  • yield *()
  • return *()
  • for _ in *(): ...

are not valid without a comma after the iterable.
These are allowed by python.gram and only rejected in the code generation step. This means that the documented Full Grammar specification is incomplete. We can do better.

Linked PRs

  • gh-156058: Disallow lone starred expressions at the grammar level #156059

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  1. encukou
    self-assigned this
    on Aug 19, 2026
  2. encukou
    added
    interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)
    on Aug 19, 2026
  3. encukou
    added a parent issue on Aug 19, 2026
    • Reword the Expressions chapter of the docs #141984
  4. encukou
    added this to docs issueson Aug 19, 2026
  5. encukou
    added
    topic-parser
    on Aug 19, 2026
  6. github-project-automation
    moved this to Todo in docs issueson Aug 19, 2026
  7. encukou
    removed a parent issue on Aug 19, 2026
    • Reword the Expressions chapter of the docs #141984
  8. encukou
    added a parent issue on Aug 19, 2026
    • Align the grammar documentation with Python's actual grammar #127833

  9. encukou commented on Aug 19, 2026

    @encukou
    encukou
    on Aug 19, 2026
    MemberAuthor
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    I'm sending a draft PR to show the change to make, as I open discussion on whether we want to make changes like this.

  10. sirosen commented on Aug 24, 2026

    @sirosen
    sirosen
    on Aug 24, 2026
    Contributor
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    It seems to work in the new comprehension syntax, unless I misunderstood the issue.

    x = [*range(5) for _ in range (3)]

    That said, no opinion from me on where or how invalid usages are caught.

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

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