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Mypy Release Notes

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Mypy 1.18

We’ve just uploaded mypy 1.18 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.

Mypy Performance Improvements

Mypy 1.18 includes numerous performance improvements, resulting in about 40% speedup compared to 1.17 when type checking mypy itself. In extreme cases, the improvement can be 10x or higher. The list below is an overview of the various mypy optimizations. Many mypyc improvements (discussed in a separate section below) also improve performance.

Type caching optimizations have a small risk of causing regressions. When reporting issues with unexpected inferred types, please also check if --disable-expression-cache will work around the issue, as it turns off some of these optimizations.

• Improve self check performance by 1.8% (Jukka Lehtosalo, PR 19768, 19769, 19770)
• Optimize fixed-format deserialization (Ivan Levkivskyi, PR 19765)
• Use macros to optimize fixed-format deserialization (Ivan Levkivskyi, PR 19757)
• Two additional micro‑optimizations (Ivan Levkivskyi, PR 19627)
• Another set of micro‑optimizations (Ivan Levkivskyi, PR 19633)
• Cache common types (Ivan Levkivskyi, PR 19621)
• Skip more method bodies in third‑party libraries for speed (Ivan Levkivskyi, PR 19586)
• Simplify the representation of callable types (Ivan Levkivskyi, PR 19580)
• Add cache for types of some expressions (Ivan Levkivskyi, PR 19505)
• Use cache for dictionary expressions (Ivan Levkivskyi, PR 19536)
• Use cache for binary operations (Ivan Levkivskyi, PR 19523)
• Cache types of type objects (Ivan Levkivskyi, PR 19514)
• Avoid duplicate work when checking boolean operations (Ivan Levkivskyi, PR 19515)
• Optimize generic inference passes (Ivan Levkivskyi, PR 19501)
• Speed up the default plugin (Jukka Lehtosalo, PRs 19385 and 19462)
• Remove nested imports from the default plugin (Ivan Levkivskyi, PR 19388)
• Micro‑optimize type expansion (Jukka Lehtosalo, PR 19461)
• Micro‑optimize type indirection (Jukka Lehtosalo, PR 19460)
• Micro‑optimize the plugin framework (Jukka Lehtosalo, PR 19464)
• Avoid temporary set creation in subtype checking (Jukka Lehtosalo, PR 19463)
• Subtype checking micro‑optimization (Jukka Lehtosalo, PR 19384)
• Return early where possible in subtype check (Stanislav Terliakov, PR 19400)
• Deduplicate some types before joining (Stanislav Terliakov, PR 19409)
• Speed up type checking by caching argument inference context (Jukka Lehtosalo, PR 19323)

... (truncated)

• 03fbaa9 bump version to 1.18.1 due to wheels failure
• b44a1fb removed +dev from version
• 7197a99 Removed Unreleased in the Changelog for Release 1.18 (#19827)
• ee61cec Updates to 1.18 changelog (#19826)
• 24eed0b Initial changelog for release 1.18 (#19818)
• 0ca1f2a Expose --fixed-format-cache if compiled (#19815)
• 2ce1bb2 [mypyc] Fix subclass processing in detect_undefined_bitmap (#19787)
• a6b55f0 feat: new mypyc primitives for weakref.proxy (#19217)
• 5a323dd Make --allow-redefinition-new argument public (#19796)
• 8638eb4 [stubtest] temporary --ignore-disjoint-bases flag (#19740)
• Additional commits viewable in compare view

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