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Update changelog for some mypy 2 changes #21279

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34 changes: 34 additions & 0 deletions CHANGELOG.md
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## Next Release

### Enabling `--local-partial-types` by default

This flag affects the inference of types based on assignments in other scopes.
For now, explicitly disabling this continues to be supported, but this support will be removed
in the future as the legacy behaviour is hard to support with other current and future features
in mypy, like the daemon or the new implementation of flexible redefinitions.

Contributed by Ivan Levkivskyi, Jukka Lehtosalo, Shantanu in [PR 21163](https://github.com/python/mypy/pull/21163)

### Enabling `--strict-bytes` by default

Per [PEP 688](https://peps.python.org/pep-0688), mypy no longer treats `bytearray` and `memoryview`
values as assignable to the `bytes` type.

Contributed by Shantanu in [PR 18371](https://github.com/python/mypy/pull/18371)

### Drop Support for Targeting Python 3.9

Mypy no longer supports type checking code with `--python-version 3.9`.
Use `--python-version 3.10` or newer.

Contributed by Shantanu, Marc Mueller in [PR 21243](https://github.com/python/mypy/pull/21243)

### Remove special casing of legacy bundled stubs

Mypy used to bundle stubs for a few packages in versions 0.812 and earlier. To navigate the
transition, mypy used to report missing types for these packages even if `--ignore-missing-imports`
was set. Mypy now consistently respects `--ignore-missing-imports` for all packages.

Contributed by Shantanu in [PR 18372](https://github.com/python/mypy/pull/18372)

### Prevent assignment to None for non-Optional class variables with type comments

Mypy used to allow assignment to None for class variables when using type comments. This was a
common idiom in Python 3.5 and earlier, prior to the introduction of variable annotations.
However, this was a soundness hole and has now been removed.

Contributed by Shantanu in [PR 20054](https://github.com/python/mypy/pull/20054)

## Mypy 1.20

We’ve just uploaded mypy 1.20.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
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