Bump mypy from 1.18.2 to 1.19.0

[dependabot]

Bumps mypy from 1.18.2 to 1.19.0.

Changelog

Sourced from mypy's changelog.

Mypy Release Notes

Next Release

Drop Support for Python 3.9

Mypy no longer supports running with Python 3.9, which has reached end-of-life. When running mypy with Python 3.10+, it is still possible to type check code that needs to support Python 3.9 with the --python-version 3.9 argument. Support for this will be dropped in the first half of 2026!

Contributed by Marc Mueller (PR 20156).

Mypy 1.19

We’ve just uploaded mypy 1.19.0 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

You can read the full documentation for this release on Read the Docs.

Python 3.9 Support Ending Soon

This is the last mypy feature release that supports Python 3.9, which reached end of life in October 2025.

Performance Improvements

• Switch to a more dynamic SCC processing logic (Ivan Levkivskyi, PR 20053)
• Speed up type aliases (Ivan Levkivskyi, PR 19810)

Fixed‑Format Cache Improvements

Mypy uses a cache by default to speed up incremental runs by reusing partial results from earlier runs. Mypy 1.18 added a new binary fixed-format cache representation as an experimental feature. The feature is no longer experimental, and we are planning to enable it by default in a future mypy release (possibly 1.20), since it's faster and uses less space than the original, JSON-based cache format. Use --fixed-format-cache to enable the fixed-format cache.

Mypy now has an extra dependency on the librt PyPI package, as it's needed for cache serialization and deserialization.

Mypy ships with a tool to convert fixed-format cache files to the old JSON format. Example of how to use this:

$ python -m mypy.exportjson .mypy_cache/.../my_module.data.ff

... (truncated)

Commits

• 0f068c9 Remove +dev
• 6d5cf52 Various updates to 1.19 changelog (#20304)
• 3c81308 Add draft version of 1.19 release notes (#20296)
• 1999a20 [mypyc] librt base64: use existing SIMD CPU dispatch by customizing build fla...
• 1b94fbb [mypyc] Fix vtable pointer with inherited dunder new (#20302)
• 13369cb [mypyc] Fix crash on super in generator (#20291)
• a087a58 Update import map when new modules added (#20271)
• 35e843c [mypyc] Add efficient librt.base64.b64decode (#20263)
• 094f66d [mypyc] Add repr to AssignmentTarget subclasses (#20258)
• 0738db3 Do not push partial types to the binder (#20202)
• Additional commits viewable in compare view

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Resolves #20304
Resolves #20296
Resolves #20302
Resolves #20291
Resolves #20271
Resolves #20263
Resolves #20258
Resolves #20202

[github-actions]

🤖 Claude Code Review

PR Code Review Analysis

Summary

This is a minor dependency version bump for mypy from 1.18.2 to 1.19.0 in the development/linting dependencies.

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Detailed Checklist Review

Code Quality

✅ Code follows style guide

• N/A - This is a dependency version change in pyproject.toml, no code logic modified

✅ No commented-out code

• No commented-out code present

✅ Meaningful variable names

• N/A - No new variables introduced

✅ DRY principle followed

• N/A - No code duplication concerns in a version bump

✅ Identify Defects

• No bugs, logic errors, or security vulnerabilities introduced
• This is a minor version bump (1.18.2 → 1.19.0) of a static type checker
• The change is isolated to the lint dependency group, used only in development
• pyproject.toml:83 - Version bump appears safe and follows semantic versioning

⚠️ Project memory configuration

• No .claude/CLAUDE.md file found in the repository to review against

Testing

⚠️ Unit tests for new functions

• N/A - No new functions added
• Note: Since this is a mypy version bump, existing code should be tested to ensure no new type checking errors are introduced

⚠️ Integration tests for new endpoints

• N/A - No new endpoints

⚠️ Edge cases covered

• N/A - Dependency version change only

⚠️ Test coverage > 80%

• Cannot determine from diff alone
• Recommendation: CI should validate that mypy 1.19.0 passes successfully on all existing code

Documentation

✅ Readme updated if needed

• Not required - internal dependency version bump doesn't affect user-facing documentation

✅ API docs updated

• Not required - no API changes

✅ Inline comments for complex logic

• N/A - No code logic changes

❌ CHANGELOG.md updated

• The CHANGELOG.md should be updated to document this dependency upgrade
• Recommendation: Add entry like "Bump mypy from 1.18.2 to 1.19.0"

Security

✅ No hardcoded credentials

• No credentials present

✅ Input validation implemented

• N/A - No new inputs

✅ Proper error handling

• N/A - No new error handling paths

✅ No sensitive data in logs

• N/A - No logging changes

✅ No license files (.lic) or AQAAAD strings

• No license files or sensitive strings in this diff

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Final Recommendation

APPROVE with minor suggestions

This is a clean, low-risk dependency version bump. The only action item is:

1. CHANGELOG.md (pyproject.toml:83) - Consider adding an entry documenting this mypy version upgrade for transparency

The change should be safe to merge once CI passes, confirming that mypy 1.19.0 doesn't introduce new type checking failures in the existing codebase.

Automated code review analyzing defects and coding standards