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p-sawicki
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Sep 11, 2025
ilevkivskyi
approved these changes
Sep 11, 2025
| ### `--allow-redefinition-new` | ||
| ### Mypy Performance Improvements | ||
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| Mypy 1.18 includes numerous performance improvements, resulting in about 38% speedup |
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IMO this is unnecessarily precise, saying ~40% may be better.
| Mypy 1.18 includes numerous performance improvements, resulting in about 38% 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. |
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Should we mention --disable-expression-cache just in case, or only advise it when people report bugs?
| convert fixed-format cache files to JSON, but details of the output JSON may be | ||
| different from the current JSON format. If you rely on being able to inspect | ||
| mypy cache files, we recommend creating a GitHub issue and explaining your use | ||
| case, so that we can more likely provide support for it. |
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Maybe also mention using MypyFile.read(data) to inspect cache, which may be sufficient for some users?
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| Mypy 1.18 includes numerous performance improvements, resulting in a 38% overall speedup compared to 1.17 | ||
| - Add `--strict-equality-for-none` to flag non-overlapping comparisons involving None (Christoph Tyralla, PR [19718](https://github.com/python/mypy/pull/19718)) | ||
| - Don’t show import‑related errors after a module‑level `assert False` (Stanislav Terliakov, PR [19347](https://github.com/python/mypy/pull/19347)) |
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Not sure if it makes sense to clarify that this is for cases like assert sys.platform == "linux" at top of file.
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| ### Experimental Free-threading Support for Mypyc | ||
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| All mypyc tests now pass on free-threading 3.14 release candidate builds. The performance |
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Suggested change
| All mypyc tests now pass on free-threading 3.14 release candidate builds. The performance | |
| All mypyc tests now pass on free-threading Python 3.14 release candidate builds. The performance |
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| ### Mypyc: Support `__new__` | ||
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| Mypyc now has rudimentary support for `__new__` methods. |
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| Mypyc now has rudimentary support for `__new__` methods. | |
| Mypyc now has rudimentary support for user-defined `__new__` methods. |
| - Avoid duplicate work when checking boolean operations (Ivan Levkivskyi, PR [19515](https://github.com/python/mypy/pull/19515)) | ||
| - Optimize generic inference passes (Ivan Levkivskyi, PR [19501](https://github.com/python/mypy/pull/19501)) | ||
| - Speed up the default plugin (Jukka Lehtosalo, PR [19462](https://github.com/python/mypy/pull/19462)) | ||
| - Speed up the default plugin (Jukka Lehtosalo, PR [19385](https://github.com/python/mypy/pull/19385)) |
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Maybe merge these two PR into single line, like few lines above?
KevinRK29
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Sep 11, 2025
Did various edits, added a few additional sections, and reordered some sections. (cherry picked from commit 73fa69e)
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Did various edits, added a few additional sections, and reordered some sections.