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Various 1.9 CHANGELOG updates
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Mostly minor, but also announce that `--local-partial-types` will
be enabled by default soon and explain type parameter defaults in
more detail.
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@JukkaL
JukkaL committed Mar 4, 2024
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Expand Up @@ -12,51 +12,92 @@ You can read the full documentation for this release on [Read the Docs](http://m

Because the version of typeshed we use in mypy 1.9 doesn't support 3.7, neither does mypy 1.9. (Jared Hance, PR [16883](https://github.com/python/mypy/pull/16883))

#### Basic PEP 696 Support
We are planning to enable *local partial types* (enabled via the
`--local-partial-types` flag) later this year by default. This change
was announced years ago, but now it's finally happening. This is a
major backward-incompatible change, so we'll probably include it as
part of the upcoming mypy 2.0 release. This makes daemon and
non-daemon mypy runs have the same behavior by default.

Local partial types can also be enabled in the mypy config file:
```
local_partial_types = True
```

We are looking at providing a tool to make it easier to migrate
projects to use `--local-partial-types`, but it's not yet clear whether
this is practical. The migration usually involves adding some
explicit type annotations to module-level and class-level variables.

#### Basic Support for Type Parameter Defaults (PEP 696)

This release contains new experimental support for type parameter
defaults ([PEP 696](https://peps.python.org/pep-0696)). Please try it
out! This feature was contributed by Marc Mueller.

Since this feature will be officially introduced in the next Python
feature release (3.13), you will need to import `TypeVar`, `ParamSpec`
or `TypeVarTuple` from `typing_extensions` to use defaults for now.

This example adapted from the PEP defines a default for `BotT`:
```python
from typing import Generic
from typing_extensions import TypeVar

class Bot: ...

BotT = TypeVar("BotT", bound=Bot, default=Bot)

This release contains new support for PEP 696 (https://peps.python.org/pep-0696). Please try it out! (Contributed by Marc Mueller).
class Context(Generic[BotT]):
bot: BotT

#### Type-checking improvements
* Fix duplicated TypeVarTuple test (Jelle Zijlstra, PR [16853](https://github.com/python/mypy/pull/16853))
class MyBot(Bot): ...

# type is Bot (the default)
reveal_type(Context().bot)
# type is MyBot
reveal_type(Context[MyBot]().bot)
```

#### Type-checking Improvements
* Fix missing type store for overloads (Marc Mueller, PR [16803](https://github.com/python/mypy/pull/16803))
* Fix `'WriteToConn' object has no attribute 'flush'` (Charlie Denton, PR [16801](https://github.com/python/mypy/pull/16801))
* Update TypeAlias error messages to remove colon (Marc Mueller, PR [16831](https://github.com/python/mypy/pull/16831))
* Support narrowing unions that include type[None] (Christoph Tyralla, PR [16315](https://github.com/python/mypy/pull/16315))
* Improve TypeAlias error messages (Marc Mueller, PR [16831](https://github.com/python/mypy/pull/16831))
* Support narrowing unions that include `type[None]` (Christoph Tyralla, PR [16315](https://github.com/python/mypy/pull/16315))
* Support TypedDict functional syntax as class base type (anniel-stripe, PR [16703](https://github.com/python/mypy/pull/16703))
* Accept multiline quoted annotations (Shantanu, PR [16765](https://github.com/python/mypy/pull/16765))
* Allow unary + in Literal (Jelle Zijlstra, PR [16729](https://github.com/python/mypy/pull/16729))
* Speed up finding function type variables (Jukka Lehtosalo, PR [16562](https://github.com/python/mypy/pull/16562))
* Allow unary + in `Literal` (Jelle Zijlstra, PR [16729](https://github.com/python/mypy/pull/16729))
* Substitute type variables in return type of static methods (Kouroche Bouchiat, PR [16670](https://github.com/python/mypy/pull/16670))
* Consider TypeVarTuple to be invariant (Marc Mueller, PR [16759](https://github.com/python/mypy/pull/16759))
* Add `alias` support to `field()` in `attrs` plugin (Nikita Sobolev, PR [16610](https://github.com/python/mypy/pull/16610))
* Improve attrs hashability detection (Tin Tvrtković, PR [16556](https://github.com/python/mypy/pull/16556))

#### Performance Improvements

* Speed up finding function type variables (Jukka Lehtosalo, PR [16562](https://github.com/python/mypy/pull/16562))

#### Documentation Updates
* Document --enable-incomplete-feature possible values in "mypy --help" (Froger David, PR [16661](https://github.com/python/mypy/pull/16661))

* Document supported values for `--enable-incomplete-feature` in "mypy --help" (Froger David, PR [16661](https://github.com/python/mypy/pull/16661))
* Update new type system discussion links (thomaswhaley, PR [16841](https://github.com/python/mypy/pull/16841))
* Docs: Add missing class instantiation to cheat sheet (Aleksi Tarvainen, PR [16817](https://github.com/python/mypy/pull/16817))
* Fix typo in getting_started.rst (zipperer, PR [16700](https://github.com/python/mypy/pull/16700))
* Add missing class instantiation to cheat sheet (Aleksi Tarvainen, PR [16817](https://github.com/python/mypy/pull/16817))
* Document how evil `--no-strict-optional` is (Shantanu, PR [16731](https://github.com/python/mypy/pull/16731))
* Improve mypy daemon documentation note about local partial types (Makonnen Makonnen, PR [16782](https://github.com/python/mypy/pull/16782))
* Fix numbering error in docs (Stefanie Molin, PR [16838](https://github.com/python/mypy/pull/16838))
* Various docs improvements (Shantanu, PR [16836](https://github.com/python/mypy/pull/16836))
* Fix numbering error (Stefanie Molin, PR [16838](https://github.com/python/mypy/pull/16838))
* Various documentation improvements (Shantanu, PR [16836](https://github.com/python/mypy/pull/16836))

#### Stubtest Improvements
* Stubtest will ignore private function/method parameters when they are missing from the stub.
Private parameters names start with a single underscore and have a default
(PR [16507](https://github.com/python/mypy/pull/16507)).
* Stubtest: ignore a new protocol dunder (Alex Waygood, PR [16895](https://github.com/python/mypy/pull/16895))
* stubtest: Private parameters can be omitted (Sebastian Rittau, PR [16507](https://github.com/python/mypy/pull/16507))
* stubtest: Add support for setting enum members to "..." (Jelle Zijlstra, PR [16807](https://github.com/python/mypy/pull/16807))
* stubtest: adjust symtable logic (Shantanu, PR [16823](https://github.com/python/mypy/pull/16823))
* stubtest: fix pos-only handling in overload resolution (Shantanu, PR [16750](https://github.com/python/mypy/pull/16750))
* Ignore private function/method parameters when they are missing from the stub (private parameter names start with a single underscore and have a default) (PR [16507](https://github.com/python/mypy/pull/16507))
* Ignore a new protocol dunder (Alex Waygood, PR [16895](https://github.com/python/mypy/pull/16895))
* Private parameters can be omitted (Sebastian Rittau, PR [16507](https://github.com/python/mypy/pull/16507))
* Add support for setting enum members to "..." (Jelle Zijlstra, PR [16807](https://github.com/python/mypy/pull/16807))
* Adjust symbol table logic (Shantanu, PR [16823](https://github.com/python/mypy/pull/16823))
* Fix posisitional-only handling in overload resolution (Shantanu, PR [16750](https://github.com/python/mypy/pull/16750))

#### Stubgen Improvements
* stubgen: Fix crash on star unpack of TypeVarTuple (Ali Hamdan, PR [16869](https://github.com/python/mypy/pull/16869))
* Fix failing stubgen tests (Ali Hamdan, PR [16779](https://github.com/python/mypy/pull/16779))
* stubgen: use PEP 604 unions everywhere (Ali Hamdan, PR [16519](https://github.com/python/mypy/pull/16519))
* Improve stubgen tests (Fabian Keller, PR [16760](https://github.com/python/mypy/pull/16760))
* stubgen: Do not ignore property deleter (Ali Hamdan, PR [16781](https://github.com/python/mypy/pull/16781))
* Fix crash on star unpack of TypeVarTuple (Ali Hamdan, PR [16869](https://github.com/python/mypy/pull/16869))
* Use PEP 604 unions everywhere (Ali Hamdan, PR [16519](https://github.com/python/mypy/pull/16519))
* Do not ignore property deleter (Ali Hamdan, PR [16781](https://github.com/python/mypy/pull/16781))
* Support type stub generation for `staticmethod` (WeilerMarcel, PR [14934](https://github.com/python/mypy/pull/14934))


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