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Changelog updates for 1.20#21109

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JukkaL wants to merge 17 commits intomasterfrom
changelog-1.20
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Changelog updates for 1.20#21109
JukkaL wants to merge 17 commits intomasterfrom
changelog-1.20

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@JukkaL
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@JukkaL JukkaL commented Mar 30, 2026

Add sections for major features and list items for small user-visible changes.

Document expected major changes in the mypy 2.0 release.

This is still not quite final, but should be close to it.

Related issue: #20726

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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

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JukkaL commented Mar 30, 2026

I'll leave this open for the rest of day in case others would like to provide feedback.

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LG, thank! Just few minor comments.

minor code changes to adopt. For more information, refer to the
[documentation](https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-strict-bytes).

Finally, `--allow-redefinition-new` will be renamed to `--allow-redefinition`. If you want
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Maybe add a super short motivation/reminder for why --allow-redefinition-new is better. E.g. mention that it supports conditional redefinition?


Also, we are planning to turn local partial types on by default in mypy 2.0 (to be
released soon), and this makes the change much less disruptive. However, explicitly
disabling local partial types will continue to be supported indefinitely.
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Actually, I am not sure about this. I would propose to deprecate and delete support for non-local partial types at some point. This is because parallel type checking will also require --local-partial-types very soon.


### Experimental New Parser

If you install mypy using `pip install mypy[native-parse]` and run mypy with
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Not sure why I named the optional dependency native-parse without r at the end. I think we should rename it to native-parser for consistency with the flag name.

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