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#Fix 21316#21473

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pranavmanglik:fix-21316
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#Fix 21316#21473
pranavmanglik wants to merge 4 commits into
python:masterfrom
pranavmanglik:fix-21316

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@pranavmanglik pranavmanglik commented May 12, 2026 •
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This change adds support for statically evaluable conditional fields in NamedTuple class syntax.

Example:

class NT(NamedTuple):
    x: int

    if sys.version_info >= (3, 12):
        y: str

Fixes #21316

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github-actions Bot commented May 13, 2026

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

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pranavmanglik commented May 13, 2026

This PR currently adds support for statically evaluable conditional fields in NamedTuple definitions.

It covers:

  • reachable/unreachable conditional branches
  • if / elif / else
  • nested conditionals
  • multiple fields inside branches
  • conditional default values
  • handling of unknown conditions

The implementation reuses existing reachability analysis via infer_condition_value.

I intentionally scoped this PR to NamedTuple support first to keep the change focused. Similar support for dataclasses and other semantic-transform-based constructs could potentially be added in follow-up work, and I’d be interested in contributing to those as well.

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Support conditional definitions in dataclasses, etc.

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