Bump mypy from 1.19.1 to 1.20.0

[dependabot]

Bumps mypy from 1.19.1 to 1.20.0.

Changelog

Sourced from mypy's changelog.

Mypy Release Notes

Next Release

Enabling --local-partial-types by default

This flag affects the inference of types based on assignments in other scopes. For now, explicitly disabling this continues to be supported, but this support will be removed in the future as the legacy behaviour is hard to support with other current and future features in mypy, like the daemon or the new implementation of flexible redefinitions.

Contributed by Ivan Levkivskyi, Jukka Lehtosalo, Shantanu in PR 21163

Enabling --strict-bytes by default

Per PEP 688, mypy no longer treats bytearray and memoryview values as assignable to the bytes type.

Contributed by Shantanu in PR 18371

Drop Support for Targeting Python 3.9

Mypy no longer supports type checking code with --python-version 3.9. Use --python-version 3.10 or newer.

Contributed by Shantanu, Marc Mueller in PR 21243

Remove special casing of legacy bundled stubs

Mypy used to bundle stubs for a few packages in versions 0.812 and earlier. To navigate the transition, mypy used to report missing types for these packages even if --ignore-missing-imports was set. Mypy now consistently respects --ignore-missing-imports for all packages.

Contributed by Shantanu in PR 18372

Prevent assignment to None for non-Optional class variables with type comments

Mypy used to allow assignment to None for class variables when using type comments. This was a common idiom in Python 3.5 and earlier, prior to the introduction of variable annotations. However, this was a soundness hole and has now been removed.

Contributed by Shantanu in PR 20054

Mypy 1.20

We’ve just uploaded mypy 1.20.0 to the Python Package Index (PyPI). Mypy is a static type checker for Python. This release includes new features, performance improvements and bug fixes. You can install it as follows:

python3 -m pip install -U mypy

... (truncated)

Commits

• 770d3ca Remove +dev from version
• 4738ffa Changelog updates for 1.20 (#21109)
• b4f07a7 Use 'native-parser' instead of 'native-parse' for optional dependency (#21115)
• 7bec7b7 [mypyc] Document librt and librt.base64 (#21114)
• c482596 --allow-redefinition-new is no longer experimental (#21110)
• c916ca3 sdist: include misc/{diff-cache,apply-cache-diff}.py for `mypy/test/test_di...
• b137e4e [mypyc] Speed up native-to-native imports within the same group (#21101)
• 978b711 [mypyc] Fix range loop variable off-by-one after loop exit (#21098)
• 67ada30 [stubtest] Check runtime availability of private types not marked `@type_chec...
• bdef6ef librt cache tests: build respecting MYPY_TEST_PREFIX (#21097)
• Additional commits viewable in compare view

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[github-actions]

🤖 Claude Code Review

PR Code Review

Change: Bump mypy from 1.19.1 to 1.20.0 in pyproject.toml

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Code Quality

• ✅ Style guide — Single-line dependency version bump, no style concerns.
• ✅ No commented-out code — N/A.
• ✅ Meaningful variable names — N/A.
• ✅ DRY principle — N/A.
• ✅ Defects — No logic errors; straightforward version pin update.
• ✅ CLAUDE.md — No issues; project config is general and environment-agnostic.

Testing

• ✅ Unit/integration tests — No new code requiring tests.
• ✅ Edge cases — N/A for a dependency bump.
• ⚠️ Test coverage — Not verifiable from the diff alone. The CI pipeline should confirm mypy 1.20.0 passes type checks without regressions.

Documentation

• ✅ README — No update needed for a dev-dependency bump.
• ✅ API docs — N/A.
• ✅ Inline comments — N/A.
• ⚠️ CHANGELOG.md — Not included in the diff. Dependency bumps are typically tracked (even if automated via Dependabot); confirm whether this project's convention requires a changelog entry.
• ✅ Markdown formatting — N/A.

Security

• ✅ No hardcoded credentials — N/A.
• ✅ Input validation — N/A.
• ✅ Error handling — N/A.
• ✅ No sensitive data in logs — N/A.
• ✅ No license files — N/A.

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Summary

This is a routine Dependabot-style bump of a lint-only dev dependency (mypy). The change is minimal and low-risk. The only items to confirm:

1. CI passes with mypy 1.20.0 (no new type errors surfaced by the updated checker).
2. Whether a CHANGELOG entry is expected per project convention.

Verdict: Approve pending green CI.

Automated code review analyzing defects and coding standards