build(deps-dev): bump mypy from 1.15.0 to 1.19.0

[dependabot]

Bumps mypy from 1.15.0 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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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	mypy@​1.15.0 ⏵ 1.19.0	+1				+20
	pathspec@​0.12.1
	librt@​0.7.4

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[socket-security]

Warning

Review the following alerts detected in dependencies.

According to your organization's Security Policy, it is recommended to resolve "Warn" alerts. Learn more about Socket for GitHub.

Action	Severity	Alert  (click "▶" to expand/collapse)
Warn		Native binaries present: pypi librt Location: Package overview From: poetry.lock → pypi/librt@0.7.4 ℹ Read more on: This package | This alert | Why is native code a concern? Next steps: Take a moment to review the security alert above. Review the linked package source code to understand the potential risk. Ensure the package is not malicious before proceeding. If you're unsure how to proceed, reach out to your security team or ask the Socket team for help at support@socket.dev. Suggestion: Verify that the inclusion of native code is expected and necessary for this package's functionality. If it is unnecessary or unexpected, consider using alternative packages without native code to mitigate potential risks. Mark the package as acceptable risk. To ignore this alert only in this pull request, reply with the comment @SocketSecurity ignore pypi/librt@0.7.4. You can also ignore all packages with @SocketSecurity ignore-all. To ignore an alert for all future pull requests, use Socket's Dashboard to change the triage state of this alert.

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[dependabot]

Superseded by #424.