build(deps): Bump mypy from 1.17.0 to 1.19.0

[dependabot]

Bumps mypy from 1.17.0 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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[codacy-production]

Pull Request Overview

This is a dependency-only bump (mypy 1.17.0 -> 1.19.0). Codacy reports the repository remains up to standards. Nothing in the diff introduces code; primary risks are changes in mypy behavior or runtime requirements (mypy 1.19 adds librt dependency and drops Python 3.9 support in future releases). These are not merge blockers but should be verified in CI.

About this PR

• Run the repository's type-checking CI job and ensure mypy passes with the new version. If your CI pins mypy separately from requirements.txt, update that pin too.
• If your project relies on mypy fixed-format cache or runs mypy in environments without librt, ensure the environment can install the librt PyPI package or avoid enabling --fixed-format-cache until the dependency is available.
• PR description contains the mypy changelog; good. Add a short note about whether CI/type-check runs are expected to change and whether the project supports Python versions compatible with mypy 1.19 (mypy no longer supports running under Python 3.9 in future releases and 1.19 adds a new librt dependency used for fixed-format cache).

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[codacy-production]

💡 Suggestion

Bumped mypy from 1.17.0 to 1.19.0 in requirements.txt. Verify CI and local developer environments install the new mypy and that type-checking output remains acceptable. No code change here, but this can change type-checker errors/warnings across the codebase.

🟡 Medium risk