Mypy

We’ve just uploaded mypy 1.10 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). 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](http://mypy.readthedocs.io).

Support TypeIs (PEP 742)

Mypy now supports `TypeIs` ([PEP 742](https://peps.python.org/pep-0742/)), which allows
functions to narrow the type of a value, similar to `isinstance()`. Unlike `TypeGuard`,
`TypeIs` can narrow in both the `if` and `else` branches of an if statement:

python
from typing_extensions import TypeIs

def is_str(s: object) -> TypeIs[str]:
return isinstance(s, str)

def f(o: str | int) -> None:
if is_str(o):
Type of o is 'str'
...
else:
Type of o is 'int'
...


`TypeIs` will be added to the `typing` module in Python 3.13, but it
can be used on earlier Python versions by importing it from
`typing_extensions`.

This feature was contributed by Jelle Zijlstra (PR [16898](https://github.com/python/mypy/pull/16898)).

Support TypeVar Defaults (PEP 696)

[PEP 696](https://peps.python.org/pep-0696/) adds support for type parameter defaults.
Example:

python
from typing import Generic
from typing_extensions import TypeVar

T = TypeVar("T", default=int)

class C(Generic[T]):
...

x: C = ...
y: C[str] = ...
reveal_type(x) C[int], because of the default
reveal_type(y) C[str]


TypeVar defaults will be added to the `typing` module in Python 3.13, but they
can be used with earlier Python releases by importing `TypeVar` from
`typing_extensions`.

This feature was contributed by Marc Mueller (PR [16878](https://github.com/python/mypy/pull/16878)
and PR [16925](https://github.com/python/mypy/pull/16925)).

Support TypeAliasType (PEP 695)
As part of the initial steps towards implementing [PEP 695](https://peps.python.org/pep-0695/), mypy now supports `TypeAliasType`.
`TypeAliasType` provides a backport of the new `type` statement in Python 3.12.

python
type ListOrSet[T] = list[T] | set[T]


is equivalent to:

python
T = TypeVar("T")
ListOrSet = TypeAliasType("ListOrSet", list[T] | set[T], type_params=(T,))


Example of use in mypy:

python
from typing_extensions import TypeAliasType, TypeVar

NewUnionType = TypeAliasType("NewUnionType", int | str)
x: NewUnionType = 42
y: NewUnionType = 'a'
z: NewUnionType = object() error: Incompatible types in assignment (expression has type "object", variable has type "int | str") [assignment]

T = TypeVar("T")
ListOrSet = TypeAliasType("ListOrSet", list[T] | set[T], type_params=(T,))
a: ListOrSet[int] = [1, 2]
b: ListOrSet[str] = {'a', 'b'}
c: ListOrSet[str] = 'test' error: Incompatible types in assignment (expression has type "str", variable has type "list[str] | set[str]") [assignment]


`TypeAliasType` was added to the `typing` module in Python 3.12, but it can be used with earlier Python releases by importing from `typing_extensions`.

This feature was contributed by Ali Hamdan (PR [16926](https://github.com/python/mypy/pull/16926), PR [17038](https://github.com/python/mypy/pull/17038) and PR [17053](https://github.com/python/mypy/pull/17053))

Detect Additional Unsafe Uses of super()

Mypy will reject unsafe uses of `super()` more consistently, when the target has a
trivial (empty) body. Example:

python
class Proto(Protocol):
def method(self) -> int: ...

class Sub(Proto):
def method(self) -> int:
return super().meth() Error (unsafe)


This feature was contributed by Shantanu (PR [16756](https://github.com/python/mypy/pull/16756)).

Stubgen Improvements
- Preserve empty tuple annotation (Ali Hamdan, PR [16907](https://github.com/python/mypy/pull/16907))
- Add support for PEP 570 positional-only parameters (Ali Hamdan, PR [16904](https://github.com/python/mypy/pull/16904))
- Replace obsolete typing aliases with builtin containers (Ali Hamdan, PR [16780](https://github.com/python/mypy/pull/16780))
- Fix generated dataclass `__init__` signature (Ali Hamdan, PR [16906](https://github.com/python/mypy/pull/16906))

Mypyc Improvements

- Provide an easier way to define IR-to-IR transforms (Jukka Lehtosalo, PR [16998](https://github.com/python/mypy/pull/16998))
- Implement lowering pass and add primitives for int (in)equality (Jukka Lehtosalo, PR [17027](https://github.com/python/mypy/pull/17027))
- Implement lowering for remaining tagged integer comparisons (Jukka Lehtosalo, PR [17040](https://github.com/python/mypy/pull/17040))
- Optimize away some bool/bit registers (Jukka Lehtosalo, PR [17022](https://github.com/python/mypy/pull/17022))
- Remangle redefined names produced by async with (Richard Si, PR [16408](https://github.com/python/mypy/pull/16408))
- Optimize TYPE_CHECKING to False at Runtime (Srinivas Lade, PR [16263](https://github.com/python/mypy/pull/16263))
- Fix compilation of unreachable comprehensions (Richard Si, PR [15721](https://github.com/python/mypy/pull/15721))
- Don't crash on non-inlinable final local reads (Richard Si, PR [15719](https://github.com/python/mypy/pull/15719))

Documentation Improvements
- Import `TypedDict` from `typing` instead of `typing_extensions` (Riccardo Di Maio, PR [16958](https://github.com/python/mypy/pull/16958))
- Add missing `mutable-override` to section title (James Braza, PR [16886](https://github.com/python/mypy/pull/16886))

Error Reporting Improvements

- Use lower-case generics more consistently in error messages (Jukka Lehtosalo, PR [17035](https://github.com/python/mypy/pull/17035))

Other Notable Changes and Fixes
- Fix incorrect inferred type when accessing descriptor on union type (Matthieu Devlin, PR [16604](https://github.com/python/mypy/pull/16604))
- Fix crash when expanding invalid `Unpack` in a `Callable` alias (Ali Hamdan, PR [17028](https://github.com/python/mypy/pull/17028))
- Fix false positive when string formatting with string enum (roberfi, PR [16555](https://github.com/python/mypy/pull/16555))
- Narrow individual items when matching a tuple to a sequence pattern (Loïc Simon, PR [16905](https://github.com/python/mypy/pull/16905))
- Fix false positive from type variable within TypeGuard or TypeIs (Evgeniy Slobodkin, PR [17071](https://github.com/python/mypy/pull/17071))
- Improve `yield from` inference for unions of generators (Shantanu, PR [16717](https://github.com/python/mypy/pull/16717))
- Fix emulating hash method logic in `attrs` classes (Hashem, PR [17016](https://github.com/python/mypy/pull/17016))
- Add reverted typeshed commit that uses `ParamSpec` for `functools.wraps` (Tamir Duberstein, PR [16942](https://github.com/python/mypy/pull/16942))
- Fix type narrowing for `types.EllipsisType` (Shantanu, PR [17003](https://github.com/python/mypy/pull/17003))
- Fix single item enum match type exhaustion (Oskari Lehto, PR [16966](https://github.com/python/mypy/pull/16966))
- Improve type inference with empty collections (Marc Mueller, PR [16994](https://github.com/python/mypy/pull/16994))
- Fix override checking for decorated property (Shantanu, PR [16856](https://github.com/python/mypy/pull/16856))
- Fix narrowing on match with function subject (Edward Paget, PR [16503](https://github.com/python/mypy/pull/16503))
- Allow `+N` within `Literal[...]` (Spencer Brown, PR [16910](https://github.com/python/mypy/pull/16910))
- Experimental: Support TypedDict within `type[...]` (Marc Mueller, PR [16963](https://github.com/python/mypy/pull/16963))
- Experimtental: Fix issue with TypedDict with optional keys in `type[...]` (Marc Mueller, PR [17068](https://github.com/python/mypy/pull/17068))

Typeshed Updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=7c8e82fe483a40ec4cb0a2505cfdb0f3e7cc81d9+0&branch=main&path=stdlib) for full list of standard library typeshed stub changes.


Acknowledgements
Thanks to all mypy contributors who contributed to this release:

- Alex Waygood
- Ali Hamdan
- Edward Paget
- Evgeniy Slobodkin
- Hashem
- hesam
- Hugo van Kemenade
- Ihor
- James Braza
- Jelle Zijlstra
- jhance
- Jukka Lehtosalo
- Loïc Simon
- Marc Mueller
- Matthieu Devlin
- Michael R. Crusoe
- Nikita Sobolev
- Oskari Lehto
- Riccardo Di Maio
- Richard Si
- roberfi
- Roman Solomatin
- Sam Xifaras
- Shantanu
- Spencer Brown
- Srinivas Lade
- Tamir Duberstein
- youkaichao

I’d also like to thank my employer, Dropbox, for supporting mypy development.

We’ve just uploaded mypy 1.9 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). 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](http://mypy.readthedocs.io).

Breaking Changes

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))

We are planning to enable
[local partial types](https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-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)

class Context(Generic[BotT]):
bot: BotT

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))
* 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))
* 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 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))
* 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 (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
* 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
* 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))

Acknowledgements

​Thanks to all mypy contributors who contributed to this release:

- Aleksi Tarvainen
- Alex Waygood
- Ali Hamdan
- anniel-stripe
- Charlie Denton
- Christoph Tyralla
- Dheeraj
- Fabian Keller
- Fabian Lewis
- Froger David
- Ihor
- Jared Hance
- Jelle Zijlstra
- Jukka Lehtosalo
- Kouroche Bouchiat
- Lukas Geiger
- Maarten Huijsmans
- Makonnen Makonnen
- Marc Mueller
- Nikita Sobolev
- Sebastian Rittau
- Shantanu
- Stefanie Molin
- Stephen Morton
- thomaswhaley
- Tin Tvrtković
- WeilerMarcel
- Wesley Collin Wright
- zipperer

I’d also like to thank my employer, Dropbox, for supporting mypy development.

We’ve just uploaded mypy 1.8 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). 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](http://mypy.readthedocs.io).

Type-checking Improvements
* Do not intersect types in isinstance checks if at least one is final (Christoph Tyralla, PR [16330](https://github.com/python/mypy/pull/16330))
* Detect that `final` class without `__bool__` cannot have falsey instances (Ilya Priven, PR [16566](https://github.com/python/mypy/pull/16566))
* Do not allow `TypedDict` classes with extra keywords (Nikita Sobolev, PR [16438](https://github.com/python/mypy/pull/16438))
* Do not allow class-level keywords for `NamedTuple` (Nikita Sobolev, PR [16526](https://github.com/python/mypy/pull/16526))
* Make imprecise constraints handling more robust (Ivan Levkivskyi, PR [16502](https://github.com/python/mypy/pull/16502))
* Fix strict-optional in extending generic TypedDict (Ivan Levkivskyi, PR [16398](https://github.com/python/mypy/pull/16398))
* Allow type ignores of PEP 695 constructs (Shantanu, PR [16608](https://github.com/python/mypy/pull/16608))
* Enable `type_check_only` support for `TypedDict` and `NamedTuple` (Nikita Sobolev, PR [16469](https://github.com/python/mypy/pull/16469))

Performance Improvements
* Add fast path to analyzing special form assignments (Jukka Lehtosalo, PR [16561](https://github.com/python/mypy/pull/16561))

Improvements to Error Reporting
* Don't show documentation links for plugin error codes (Ivan Levkivskyi, PR [16383](https://github.com/python/mypy/pull/16383))
* Improve error messages for `super` checks and add more tests (Nikita Sobolev, PR [16393](https://github.com/python/mypy/pull/16393))
* Add error code for mutable covariant override (Ivan Levkivskyi, PR [16399](https://github.com/python/mypy/pull/16399))

Stubgen Improvements
* Preserve simple defaults in function signatures (Ali Hamdan, PR [15355](https://github.com/python/mypy/pull/15355))
* Include `__all__` in output (Jelle Zijlstra, PR [16356](https://github.com/python/mypy/pull/16356))
* Fix stubgen regressions with pybind11 and mypy 1.7 (Chad Dombrova, PR [16504](https://github.com/python/mypy/pull/16504))

Stubtest Improvements
* Improve handling of unrepresentable defaults (Jelle Zijlstra, PR [16433](https://github.com/python/mypy/pull/16433))
* Print more helpful errors if a function is missing from stub (Alex Waygood, PR [16517](https://github.com/python/mypy/pull/16517))
* Support `type_check_only` decorator (Nikita Sobolev, PR [16422](https://github.com/python/mypy/pull/16422))
* Warn about missing `__del__` (Shantanu, PR [16456](https://github.com/python/mypy/pull/16456))
* Fix crashes with some uses of `final` and `deprecated` (Shantanu, PR [16457](https://github.com/python/mypy/pull/16457))

Fixes to Crashes
* Fix crash with type alias to `Callable[[Unpack[Tuple[Any, ...]]], Any]` (Alex Waygood, PR [16541](https://github.com/python/mypy/pull/16541))
* Fix crash on TypeGuard in `__call__` (Ivan Levkivskyi, PR [16516](https://github.com/python/mypy/pull/16516))
* Fix crash on invalid enum in method (Ivan Levkivskyi, PR [16511](https://github.com/python/mypy/pull/16511))
* Fix crash on unimported Any in TypedDict (Ivan Levkivskyi, PR [16510](https://github.com/python/mypy/pull/16510))

Documentation Updates
* Update soft-error-limit default value to -1 (Sveinung Gundersen, PR [16542](https://github.com/python/mypy/pull/16542))
* Support Sphinx 7.x (Michael R. Crusoe, PR [16460](https://github.com/python/mypy/pull/16460))

Other Notable Changes and Fixes
* Allow mypy to output a junit file with per-file results (Matthew Wright, PR [16388](https://github.com/python/mypy/pull/16388))

Typeshed Updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=4a854366e03dee700109f8e758a08b2457ea2f51+0&branch=main&path=stdlib) for full list of standard library typeshed stub changes.

Acknowledgements

​Thanks to all mypy contributors who contributed to this release:

- Alex Waygood
- Ali Hamdan
- Chad Dombrova
- Christoph Tyralla
- Ilya Priven
- Ivan Levkivskyi
- Jelle Zijlstra
- Jukka Lehtosalo
- Marcel Telka
- Matthew Wright
- Michael R. Crusoe
- Nikita Sobolev
- Ole Peder Brandtzæg
- robjhornby
- Shantanu
- Sveinung Gundersen
- Valentin Stanciu

I’d also like to thank my employer, Dropbox, for supporting mypy development.

Posted by Wesley Collin Wright

We’ve just uploaded mypy 1.7 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). 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](http://mypy.readthedocs.io).

Using TypedDict for `**kwargs` Typing

Mypy now has support for using `Unpack[...]` with a TypedDict type to annotate `**kwargs` arguments enabled by default. Example:

python
Or 'from typing_extensions import ...'
from typing import TypedDict, Unpack

class Person(TypedDict):
name: str
age: int

def foo(**kwargs: Unpack[Person]) -> None:
...

foo(name="x", age=1) Ok
foo(name=1) Error


The definition of `foo` above is equivalent to the one below, with keyword-only arguments `name` and `age`:

python
def foo(*, name: str, age: int) -> None:
...


Refer to [PEP 692](https://peps.python.org/pep-0692/) for more information. Note that unlike in the current version of the PEP, mypy always treats signatures with `Unpack[SomeTypedDict]` as equivalent to their expanded forms with explicit keyword arguments, and there aren't special type checking rules for TypedDict arguments.

This was contributed by Ivan Levkivskyi back in 2022 (PR [13471](https://github.com/python/mypy/pull/13471)).

TypeVarTuple Support Enabled (Experimental)

Mypy now has support for variadic generics (TypeVarTuple) enabled by default, as an experimental feature. Refer to [PEP 646](https://peps.python.org/pep-0646/) for the details.

TypeVarTuple was implemented by Jared Hance and Ivan Levkivskyi over several mypy releases, with help from Jukka Lehtosalo.

Changes included in this release:

* Fix handling of tuple type context with unpacks (Ivan Levkivskyi, PR [16444](https://github.com/python/mypy/pull/16444))
* Handle TypeVarTuples when checking overload constraints (robjhornby, PR [16428](https://github.com/python/mypy/pull/16428))
* Enable Unpack/TypeVarTuple support (Ivan Levkivskyi, PR [16354](https://github.com/python/mypy/pull/16354))
* Fix crash on unpack call special-casing (Ivan Levkivskyi, PR [16381](https://github.com/python/mypy/pull/16381))
* Some final touches for variadic types support (Ivan Levkivskyi, PR [16334](https://github.com/python/mypy/pull/16334))
* Support PEP-646 and PEP-692 in the same callable (Ivan Levkivskyi, PR [16294](https://github.com/python/mypy/pull/16294))
* Support new `*` syntax for variadic types (Ivan Levkivskyi, PR [16242](https://github.com/python/mypy/pull/16242))
* Correctly handle variadic instances with empty arguments (Ivan Levkivskyi, PR [16238](https://github.com/python/mypy/pull/16238))
* Correctly handle runtime type applications of variadic types (Ivan Levkivskyi, PR [16240](https://github.com/python/mypy/pull/16240))
* Support variadic tuple packing/unpacking (Ivan Levkivskyi, PR [16205](https://github.com/python/mypy/pull/16205))
* Better support for variadic calls and indexing (Ivan Levkivskyi, PR [16131](https://github.com/python/mypy/pull/16131))
* Subtyping and inference of user-defined variadic types (Ivan Levkivskyi, PR [16076](https://github.com/python/mypy/pull/16076))
* Complete type analysis of variadic types (Ivan Levkivskyi, PR [15991](https://github.com/python/mypy/pull/15991))

New Way of Installing Mypyc Dependencies

If you want to install package dependencies needed by mypyc (not just mypy), you should now install `mypy[mypyc]` instead of just `mypy`:


python3 -m pip install -U 'mypy[mypyc]'


Mypy has many more users than mypyc, so always installing mypyc dependencies would often bring unnecessary dependencies.

This change was contributed by Shantanu (PR [16229](https://github.com/python/mypy/pull/16229)).

New Rules for Re-exports

Mypy no longer considers an import such as `import a.b as b` as an explicit re-export. The old behavior was arguably inconsistent and surprising. This may impact some stub packages, such as older versions of `types-six`. You can change the import to `from a import b as b`, if treating the import as a re-export was intentional.

This change was contributed by Anders Kaseorg (PR [14086](https://github.com/python/mypy/pull/14086)).

Improved Type Inference

The new type inference algorithm that was recently introduced to mypy (but was not enabled by default) is now enabled by default. It improves type inference of calls to generic callables where an argument is also a generic callable, in particular. You can use `--old-type-inference` to disable the new behavior.

The new algorithm can (rarely) produce different error messages, different error codes, or errors reported on different lines. This is more likely in cases where generic types were used incorrectly.

The new type inference algorithm was contributed by Ivan Levkivskyi. PR [16345](https://github.com/python/mypy/pull/16345) enabled it by default.

Narrowing Tuple Types Using len()

Mypy now can narrow tuple types using `len()` checks. Example:

python
def f(t: tuple[int, int] | tuple[int, int, int]) -> None:
if len(t) == 2:
a, b = t Ok
...


This feature was contributed by Ivan Levkivskyi (PR [16237](https://github.com/python/mypy/pull/16237)).

More Precise Tuple Lengths (Experimental)

Mypy supports experimental, more precise checking of tuple type lengths through `--enable-incomplete-feature=PreciseTupleTypes`. Refer to the [documentation](https://mypy.readthedocs.io/en/latest/command_line.html#enabling-incomplete-experimental-features) for more information.

More generally, we are planning to use `--enable-incomplete-feature` to introduce experimental features that would benefit from community feedback.

This feature was contributed by Ivan Levkivskyi (PR [16237](https://github.com/python/mypy/pull/16237)).

Mypy Changelog

We now maintain a [changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md) in the mypy Git repository. It mirrors the contents of [mypy release blog posts](https://mypy-lang.blogspot.com/). We will continue to also publish release blog posts. In the future, release blog posts will be created based on the changelog near a release date.

This was contributed by Shantanu (PR [16280](https://github.com/python/mypy/pull/16280)).

Mypy Daemon Improvements

* Fix daemon crash caused by deleted submodule (Jukka Lehtosalo, PR [16370](https://github.com/python/mypy/pull/16370))
* Fix file reloading in dmypy with --export-types (Ivan Levkivskyi, PR [16359](https://github.com/python/mypy/pull/16359))
* Fix dmypy inspect on Windows (Ivan Levkivskyi, PR [16355](https://github.com/python/mypy/pull/16355))
* Fix dmypy inspect for namespace packages (Ivan Levkivskyi, PR [16357](https://github.com/python/mypy/pull/16357))
* Fix return type change to optional in generic function (Jukka Lehtosalo, PR [16342](https://github.com/python/mypy/pull/16342))
* Fix daemon false positives related to module-level `__getattr__` (Jukka Lehtosalo, PR [16292](https://github.com/python/mypy/pull/16292))
* Fix daemon crash related to ABCs (Jukka Lehtosalo, PR [16275](https://github.com/python/mypy/pull/16275))
* Stream dmypy output instead of dumping everything at the end (Valentin Stanciu, PR [16252](https://github.com/python/mypy/pull/16252))
* Make sure all dmypy errors are shown (Valentin Stanciu, PR [16250](https://github.com/python/mypy/pull/16250))

Mypyc Improvements

* Generate error on duplicate function definitions (Jukka Lehtosalo, PR [16309](https://github.com/python/mypy/pull/16309))
* Don't crash on unreachable statements (Jukka Lehtosalo, PR [16311](https://github.com/python/mypy/pull/16311))
* Avoid cyclic reference in nested functions (Jukka Lehtosalo, PR [16268](https://github.com/python/mypy/pull/16268))
* Fix direct `__dict__` access on inner functions in new Python (Shantanu, PR [16084](https://github.com/python/mypy/pull/16084))
* Make tuple packing and unpacking more efficient (Jukka Lehtosalo, PR [16022](https://github.com/python/mypy/pull/16022))

Improvements to Error Reporting

* Update starred expression error message to match CPython (Cibin Mathew, PR [16304](https://github.com/python/mypy/pull/16304))
* Fix error code of "Maybe you forgot to use await" note (Jelle Zijlstra, PR [16203](https://github.com/python/mypy/pull/16203))
* Use error code `[unsafe-overload]` for unsafe overloads, instead of `[misc]` (Randolf Scholz, PR [16061](https://github.com/python/mypy/pull/16061))
* Reword the error message related to void functions (Albert Tugushev, PR [15876](https://github.com/python/mypy/pull/15876))
* Represent bottom type as Never in messages (Shantanu, PR [15996](https://github.com/python/mypy/pull/15996))
* Add hint for AsyncIterator incompatible return type (Ilya Priven, PR [15883](https://github.com/python/mypy/pull/15883))
* Don't suggest stubs packages where the runtime package now ships with types (Alex Waygood, PR [16226](https://github.com/python/mypy/pull/16226))

Performance Improvements

* Speed up type argument checking (Jukka Lehtosalo, PR [16353](https://github.com/python/mypy/pull/16353))
* Add fast path for checking self types (Jukka Lehtosalo, PR [16352](https://github.com/python/mypy/pull/16352))
* Cache information about whether file is typeshed file (Jukka Lehtosalo, PR [16351](https://github.com/python/mypy/pull/16351))
* Skip expensive `repr()` in logging call when not needed (Jukka Lehtosalo, PR [16350](https://github.com/python/mypy/pull/16350))

Attrs and Dataclass Improvements

* `dataclass.replace`: Allow transformed classes (Ilya Priven, PR [15915](https://github.com/python/mypy/pull/15915))
* `dataclass.replace`: Fall through to typeshed signature (Ilya Priven, PR [15962](https://github.com/python/mypy/pull/15962))
* Document `dataclass_transform` behavior (Ilya Priven, PR [16017](https://github.com/python/mypy/pull/16017))
* `attrs`: Remove fields type check (Ilya Priven, PR [15983](https://github.com/python/mypy/pull/15983))
* `attrs`, `dataclasses`: Don't enforce slots when base class doesn't (Ilya Priven, PR [15976](https://github.com/python/mypy/pull/15976))
* Fix crash on dataclass field / property collision (Nikita Sobolev, PR [16147](https://github.com/python/mypy/pull/16147))

Stubgen Improvements

* Write stubs with utf-8 encoding (Jørgen Lind, PR [16329](https://github.com/python/mypy/pull/16329))
* Fix missing property setter in semantic analysis mode (Ali Hamdan, PR [16303](https://github.com/python/mypy/pull/16303))
* Unify C extension and pure python stub generators with object oriented design (Chad Dombrova, PR [15770](https://github.com/python/mypy/pull/15770))
* Multiple fixes to the generated imports (Ali Hamdan, PR [15624](https://github.com/python/mypy/pull/15624))
* Generate valid dataclass stubs (Ali Hamdan, PR [15625](https://github.com/python/mypy/pull/15625))

Fixes to Crashes

* Fix incremental mode crash on TypedDict in method (Ivan Levkivskyi, PR [16364](https://github.com/python/mypy/pull/16364))
* Fix crash on star unpack in TypedDict (Ivan Levkivskyi, PR [16116](https://github.com/python/mypy/pull/16116))
* Fix crash on malformed TypedDict in incremental mode (Ivan Levkivskyi, PR [16115](https://github.com/python/mypy/pull/16115))
* Fix crash with report generation on namespace packages (Shantanu, PR [16019](https://github.com/python/mypy/pull/16019))
* Fix crash when parsing error code config with typo (Shantanu, PR [16005](https://github.com/python/mypy/pull/16005))
* Fix `__post_init__()` internal error (Ilya Priven, PR [16080](https://github.com/python/mypy/pull/16080))

Documentation Updates

* Make it easier to copy commands from README (Hamir Mahal, PR [16133](https://github.com/python/mypy/pull/16133))
* Document and rename `[overload-overlap]` error code (Shantanu, PR [16074](https://github.com/python/mypy/pull/16074))
* Document `--force-uppercase-builtins` and `--force-union-syntax` (Nikita Sobolev, PR [16049](https://github.com/python/mypy/pull/16049))
* Document `force_union_syntax` and `force_uppercase_builtins` (Nikita Sobolev, PR [16048](https://github.com/python/mypy/pull/16048))
* Document we're not tracking relationships between symbols (Ilya Priven, PR [16018](https://github.com/python/mypy/pull/16018))

Other Notable Changes and Fixes

* Propagate narrowed types to lambda expressions (Ivan Levkivskyi, PR [16407](https://github.com/python/mypy/pull/16407))
* Avoid importing from `setuptools._distutils` (Shantanu, PR [16348](https://github.com/python/mypy/pull/16348))
* Delete recursive aliases flags (Ivan Levkivskyi, PR [16346](https://github.com/python/mypy/pull/16346))
* Properly use proper subtyping for callables (Ivan Levkivskyi, PR [16343](https://github.com/python/mypy/pull/16343))
* Use upper bound as inference fallback more consistently (Ivan Levkivskyi, PR [16344](https://github.com/python/mypy/pull/16344))
* Add `[unimported-reveal]` error code (Nikita Sobolev, PR [16271](https://github.com/python/mypy/pull/16271))
* Add `|=` and `|` operators support for `TypedDict` (Nikita Sobolev, PR [16249](https://github.com/python/mypy/pull/16249))
* Clarify variance convention for Parameters (Ivan Levkivskyi, PR [16302](https://github.com/python/mypy/pull/16302))
* Correctly recognize `typing_extensions.NewType` (Ganden Schaffner, PR [16298](https://github.com/python/mypy/pull/16298))
* Fix partially defined in the case of missing type maps (Shantanu, PR [15995](https://github.com/python/mypy/pull/15995))
* Use SPDX license identifier (Nikita Sobolev, PR [16230](https://github.com/python/mypy/pull/16230))
* Make `__qualname__` and `__module__` available in class bodies (Anthony Sottile, PR [16215](https://github.com/python/mypy/pull/16215))
* stubtest: Hint when args in stub need to be keyword-only (Alex Waygood, PR [16210](https://github.com/python/mypy/pull/16210))
* Tuple slice should not propagate fallback (Thomas Grainger, PR [16154](https://github.com/python/mypy/pull/16154))
* Fix cases of type object handling for overloads (Shantanu, PR [16168](https://github.com/python/mypy/pull/16168))
* Fix walrus interaction with empty collections (Ivan Levkivskyi, PR [16197](https://github.com/python/mypy/pull/16197))
* Use type variable bound when it appears as actual during inference (Ivan Levkivskyi, PR [16178](https://github.com/python/mypy/pull/16178))
* Use upper bounds as fallback solutions for inference (Ivan Levkivskyi, PR [16184](https://github.com/python/mypy/pull/16184))
* Special-case type inference of empty collections (Ivan Levkivskyi, PR [16122](https://github.com/python/mypy/pull/16122))
* Allow TypedDict unpacking in Callable types (Ivan Levkivskyi, PR [16083](https://github.com/python/mypy/pull/16083))
* Fix inference for overloaded `__call__` with generic self (Shantanu, PR [16053](https://github.com/python/mypy/pull/16053))
* Call dynamic class hook on generic classes (Petter Friberg, PR [16052](https://github.com/python/mypy/pull/16052))
* Preserve implicitly exported types via attribute access (Shantanu, PR [16129](https://github.com/python/mypy/pull/16129))
* Fix a stubtest bug (Alex Waygood)
* Fix `tuple[Any, ...]` subtyping (Shantanu, PR [16108](https://github.com/python/mypy/pull/16108))
* Lenient handling of trivial Callable suffixes (Ivan Levkivskyi, PR [15913](https://github.com/python/mypy/pull/15913))
* Add `add_overloaded_method_to_class` helper for plugins (Nikita Sobolev, PR [16038](https://github.com/python/mypy/pull/16038))
* Bundle `misc/proper_plugin.py` as a part of `mypy` (Nikita Sobolev, PR [16036](https://github.com/python/mypy/pull/16036))
* Fix `case Any()` in match statement (DS/Charlie, PR [14479](https://github.com/python/mypy/pull/14479))
* Make iterable logic more consistent (Shantanu, PR [16006](https://github.com/python/mypy/pull/16006))
* Fix inference for properties with `__call__` (Shantanu, PR [15926](https://github.com/python/mypy/pull/15926))

Typeshed Updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=4a854366e03dee700109f8e758a08b2457ea2f51+0&branch=main&path=stdlib) for full list of standard library typeshed stub changes.

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

* Albert Tugushev
* Alex Waygood
* Ali Hamdan
* Anders Kaseorg
* Anthony Sottile
* Chad Dombrova
* Cibin Mathew
* dinaldoap
* DS/Charlie
* Eli Schwartz
* Ganden Schaffner
* Hamir Mahal
* Ihor
* Ikko Eltociear Ashimine
* Ilya Priven
* Ivan Levkivskyi
* Jelle Zijlstra
* Jukka Lehtosalo
* Jørgen Lind
* KotlinIsland
* Matt Bogosian
* Nikita Sobolev
* Petter Friberg
* Randolf Scholz
* Shantanu
* Thomas Grainger
* Valentin Stanciu

I’d also like to thank my employer, Dropbox, for supporting mypy development.

Posted by Jukka Lehtosalo

[Tuesday, 10 October 2023](https://mypy-lang.blogspot.com/2023/10/mypy-16-released.html)

We’ve just uploaded mypy 1.6 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). 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](http://mypy.readthedocs.io).

Introduce Error Subcodes for Import Errors

Mypy now uses the error code import-untyped if an import targets an installed library that doesn’t support static type checking, and no stub files are available. Other invalid imports produce the import-not-found error code. They both are subcodes of the import error code, which was previously used for both kinds of import-related errors.

Use \--disable-error-code=import-untyped to only ignore import errors about installed libraries without stubs. This way mypy will still report errors about typos in import statements, for example.

If you use \--warn-unused-ignore or \--strict, mypy will complain if you use \ type: ignore\[import\] to ignore an import error. You are expected to use one of the more specific error codes instead. Otherwise, ignoring the import error code continues to silence both errors.

This feature was contributed by Shantanu (PR [15840](https://github.com/python/mypy/pull/15840), PR [14740](https://github.com/python/mypy/pull/14740)).

Remove Support for Targeting Python 3.6 and Earlier

Running mypy with \--python-version 3.6, for example, is no longer supported. Python 3.6 hasn’t been properly supported by mypy for some time now, and this makes it explicit. This was contributed by Nikita Sobolev (PR [15668](https://github.com/python/mypy/pull/15668)).

Selective Filtering of \--disallow-untyped-calls Targets

Using \--disallow-untyped-calls could be annoying when using libraries with missing type information, as mypy would generate many errors about code that uses the library. Now you can use \--untyped-calls-exclude=acme, for example, to disable these errors about calls targeting functions defined in the acme package. Refer to the [documentation](https://mypy.readthedocs.io/en/latest/command_line.html#cmdoption-mypy-untyped-calls-exclude) for more information.

This feature was contributed by Ivan Levkivskyi (PR [15845](https://github.com/python/mypy/pull/15845)).

Improved Type Inference between Callable Types

Mypy now does a better job inferring type variables inside arguments of callable types. For example, this code fragment now type checks correctly:

python
def f(c: Callable[[T, S], None]) -> Callable[[str, T, S], None]: ...
def g(*x: int) -> None: ...

reveal_type(f(g)) Callable[[str, int, int], None]


This was contributed by Ivan Levkivskyi (PR [15910](https://github.com/python/mypy/pull/15910)).

Don’t Consider None and TypeVar to Overlap in Overloads

Mypy now doesn’t consider an overload item with an argument type None to overlap with a type variable:

python
overload
def f(x: None) -> None: ..
overload
def f(x: T) -> Foo[T]: ...
...


Previously mypy would generate an error about the definition of f above. This is slightly unsafe if the upper bound of T is object, since the value of the type variable could be None. We relaxed the rules a little, since this solves a common issue.

This feature was contributed by Ivan Levkivskyi (PR [15846](https://github.com/python/mypy/pull/15846)).

Improvements to \--new-type-inference

The experimental new type inference algorithm (polymorphic inference) introduced as an opt-in feature in mypy 1.5 has several improvements:

* Improve transitive closure computation during constraint solving (Ivan Levkivskyi, PR [15754](https://github.com/python/mypy/pull/15754))
* Add support for upper bounds and values with \--new-type-inference (Ivan Levkivskyi, PR [15813](https://github.com/python/mypy/pull/15813))
* Basic support for variadic types with \--new-type-inference (Ivan Levkivskyi, PR [15879](https://github.com/python/mypy/pull/15879))
* Polymorphic inference: support for parameter specifications and lambdas (Ivan Levkivskyi, PR [15837](https://github.com/python/mypy/pull/15837))
* Invalidate cache when adding \--new-type-inference (Marc Mueller, PR [16059](https://github.com/python/mypy/pull/16059))

**Note:** We are planning to enable \--new-type-inference by default in mypy 1.7. Please try this out and let us know if you encounter any issues.

ParamSpec Improvements

* Support self-types containing ParamSpec (Ivan Levkivskyi, PR [15903](https://github.com/python/mypy/pull/15903))
* Allow “…” in Concatenate, and clean up ParamSpec literals (Ivan Levkivskyi, PR [15905](https://github.com/python/mypy/pull/15905))
* Fix ParamSpec inference for callback protocols (Ivan Levkivskyi, PR [15986](https://github.com/python/mypy/pull/15986))
* Infer ParamSpec constraint from arguments (Ivan Levkivskyi, PR [15896](https://github.com/python/mypy/pull/15896))
* Fix crash on invalid type variable with ParamSpec (Ivan Levkivskyi, PR [15953](https://github.com/python/mypy/pull/15953))
* Fix subtyping between ParamSpecs (Ivan Levkivskyi, PR [15892](https://github.com/python/mypy/pull/15892))

Stubgen Improvements

* Add option to include docstrings with stubgen (chylek, PR [13284](https://github.com/python/mypy/pull/13284))
* Add required ... initializer to NamedTuple fields with default values (Nikita Sobolev, PR [15680](https://github.com/python/mypy/pull/15680))

Stubtest Improvements

* Fix \_\_mypy-replace false positives (Alex Waygood, PR [15689](https://github.com/python/mypy/pull/15689))
* Fix edge case for bytes enum subclasses (Alex Waygood, PR [15943](https://github.com/python/mypy/pull/15943))
* Generate error if typeshed is missing modules from the stdlib (Alex Waygood, PR [15729](https://github.com/python/mypy/pull/15729))
* Fixes to new check for missing stdlib modules (Alex Waygood, PR [15960](https://github.com/python/mypy/pull/15960))
* Fix stubtest enum.Flag edge case (Alex Waygood, PR [15933](https://github.com/python/mypy/pull/15933))

Documentation Improvements

* Do not advertise to create your own assert\_never helper (Nikita Sobolev, PR [15947](https://github.com/python/mypy/pull/15947))
* Fix all the missing references found within the docs (Albert Tugushev, PR [15875](https://github.com/python/mypy/pull/15875))
* Document await-not-async error code (Shantanu, PR [15858](https://github.com/python/mypy/pull/15858))
* Improve documentation of disabling error codes (Shantanu, PR [15841](https://github.com/python/mypy/pull/15841))

Other Notable Changes and Fixes

* Make unsupported PEP 695 features (introduced in Python 3.12) give a reasonable error message (Shantanu, PR [16013](https://github.com/python/mypy/pull/16013))
* Remove the \--py2 command-line argument (Marc Mueller, PR [15670](https://github.com/python/mypy/pull/15670))
* Change empty tuple from tuple\[\] to tuple\[()\] in error messages (Nikita Sobolev, PR [15783](https://github.com/python/mypy/pull/15783))
* Fix assert\_type failures when some nodes are deferred (Nikita Sobolev, PR [15920](https://github.com/python/mypy/pull/15920))
* Generate error on unbound TypeVar with values (Nikita Sobolev, PR [15732](https://github.com/python/mypy/pull/15732))
* Fix over-eager types-google-cloud-ndb suggestion (Shantanu, PR [15347](https://github.com/python/mypy/pull/15347))
* Fix type narrowing of \== None and in (None,) conditions (Marti Raudsepp, PR [15760](https://github.com/python/mypy/pull/15760))
* Fix inference for attrs.fields (Shantanu, PR [15688](https://github.com/python/mypy/pull/15688))
* Make “await in non-async function” a non-blocking error and give it an error code (Gregory Santosa, PR [15384](https://github.com/python/mypy/pull/15384))
* Add basic support for decorated overloads (Ivan Levkivskyi, PR [15898](https://github.com/python/mypy/pull/15898))
* Fix TypeVar regression with self types (Ivan Levkivskyi, PR [15945](https://github.com/python/mypy/pull/15945))
* Add \_\_match\_args\_\_ to dataclasses with no fields (Ali Hamdan, PR [15749](https://github.com/python/mypy/pull/15749))
* Include stdout and stderr in dmypy verbose output (Valentin Stanciu, PR [15881](https://github.com/python/mypy/pull/15881))
* Improve match narrowing and reachability analysis (Shantanu, PR [15882](https://github.com/python/mypy/pull/15882))
* Support \_\_bool\_\_ with Literal in \--warn-unreachable (Jannic Warken, PR [15645](https://github.com/python/mypy/pull/15645))
* Fix inheriting from generic frozen attrs class (Ilya Priven, PR [15700](https://github.com/python/mypy/pull/15700))
* Correctly narrow types for tuple\[type\[X\], ...\] (Nikita Sobolev, PR [15691](https://github.com/python/mypy/pull/15691))
* Don't flag intentionally empty generators unreachable (Ilya Priven, PR [15722](https://github.com/python/mypy/pull/15722))
* Add tox.ini to mypy sdist (Marcel Telka, PR [15853](https://github.com/python/mypy/pull/15853))
* Fix mypyc regression with pretty (Shantanu, PR [16124](https://github.com/python/mypy/pull/16124))

Typeshed Updates

Typeshed is now modular and distributed as separate PyPI packages for everything except the standard library stubs. Please see [git log](https://github.com/python/typeshed/commits/main?after=6a8d653a671925b0a3af61729ff8cf3f90c9c662+0&branch=main&path=stdlib) for full list of typeshed changes.

Acknowledgements

Thanks to Max Murin, who did most of the release manager work for this release (I just did the final steps).

Thanks to all mypy contributors who contributed to this release:

* Albert Tugushev
* Alex Waygood
* Ali Hamdan
* chylek
* EXPLOSION
* Gregory Santosa
* Ilya Priven
* Ivan Levkivskyi
* Jannic Warken
* KotlinIsland
* Marc Mueller
* Marcel Johannesmann
* Marcel Telka
* Mark Byrne
* Marti Raudsepp
* Max Murin
* Nikita Sobolev
* Shantanu
* Valentin Stanciu

Posted by Jukka Lehtosalo

[Thursday, 10 August 2023](https://mypy-lang.blogspot.com/2023/08/mypy-15-released.html)

We’ve just uploaded mypy 1.5 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)). Mypy is a static type checker for Python. This release includes new features, deprecations 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](http://mypy.readthedocs.io).

Drop Support for Python 3.7

Mypy no longer supports running with Python 3.7, which has reached end-of-life. This was contributed by Shantanu (PR [15566](https://github.com/python/mypy/pull/15566)).

Optional Check to Require Explicit override

If you enable the explicit-override error code, mypy will generate an error if a method override doesn’t use the typing.override decorator (as discussed in [PEP 698](https://peps.python.org/pep-0698/#strict-enforcement-per-project)). This way mypy will detect accidentally introduced overrides. Example:

python
mypy: enable-error-code="explicit-override"

from typing_extensions import override

class C:
def foo(self) -> None: pass
def bar(self) -> None: pass

class D(C):
Error: Method "foo" is not using override but is
overriding a method
def foo(self) -> None:
...

override
def bar(self) -> None: OK
...


You can enable the error code via \--enable-error-code=explicit-override on the mypy command line or enable\_error\_code = explicit-override in the mypy config file.

The override decorator will be available in typing in Python 3.12, but you can also use the backport from a recent version of `typing_extensions` on all supported Python versions.

This feature was contributed by Marc Mueller(PR [15512](https://github.com/python/mypy/pull/15512)).

More Flexible TypedDict Creation and Update

Mypy was previously overly strict when type checking TypedDict creation and update operations. Though these checks were often technically correct, they sometimes triggered for apparently valid code. These checks have now been relaxed by default. You can enable stricter checking by using the new \--extra-checks flag.

Construction using the `**` syntax is now more flexible:

python
from typing import TypedDict

class A(TypedDict):
foo: int
bar: int

class B(TypedDict):
foo: int

a: A = {"foo": 1, "bar": 2}
b: B = {"foo": 3}
a2: A = { **a, **b} OK (previously an error)


You can also call update() with a TypedDict argument that contains a subset of the keys in the updated TypedDict:
python
a.update(b) OK (previously an error)


This feature was contributed by Ivan Levkivskyi (PR [15425](https://github.com/python/mypy/pull/15425)).

Deprecated Flag: \--strict-concatenate

The behavior of \--strict-concatenate is now included in the new \--extra-checks flag, and the old flag is deprecated.

Optionally Show Links to Error Code Documentation

If you use \--show-error-code-links, mypy will add documentation links to (many) reported errors. The links are not shown for error messages that are sufficiently obvious, and they are shown once per error code only.

Example output:

a.py:1: error: Need type annotation for "foo" (hint: "x: List[<type>] = ...") [var-annotated]
a.py:1: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-var-annotated for more info

This was contributed by Ivan Levkivskyi (PR [15449](https://github.com/python/mypy/pull/15449)).

Consistently Avoid Type Checking Unreachable Code

If a module top level has unreachable code, mypy won’t type check the unreachable statements. This is consistent with how functions behave. The behavior of \--warn-unreachable is also more consistent now.

This was contributed by Ilya Priven (PR [15386](https://github.com/python/mypy/pull/15386)).

Experimental Improved Type Inference for Generic Functions

You can use \--new-type-inference to opt into an experimental new type inference algorithm. It fixes issues when calling a generic functions with an argument that is also a generic function, in particular. This current implementation is still incomplete, but we encourage trying it out and reporting bugs if you encounter regressions. We are planning to enable the new algorithm by default in a future mypy release.

This feature was contributed by Ivan Levkivskyi (PR [15287](https://github.com/python/mypy/pull/15287)).

Partial Support for Python 3.12

Mypy and mypyc now support running on recent Python 3.12 development versions. Not all new Python 3.12 features are supported, and we don’t ship compiled wheels for Python 3.12 yet.

* Fix ast warnings for Python 3.12 (Nikita Sobolev, PR [15558](https://github.com/python/mypy/pull/15558))
* mypyc: Fix multiple inheritance with a protocol on Python 3.12 (Jukka Lehtosalo, PR [15572](https://github.com/python/mypy/pull/15572))
* mypyc: Fix self-compilation on Python 3.12 (Jukka Lehtosalo, PR [15582](https://github.com/python/mypy/pull/15582))
* mypyc: Fix 3.12 issue with pickling of instances with \_\_dict\_\_ (Jukka Lehtosalo, PR [15574](https://github.com/python/mypy/pull/15574))
* mypyc: Fix i16 on Python 3.12 (Jukka Lehtosalo, PR [15510](https://github.com/python/mypy/pull/15510))
* mypyc: Fix int operations on Python 3.12 (Jukka Lehtosalo, PR [15470](https://github.com/python/mypy/pull/15470))
* mypyc: Fix generators on Python 3.12 (Jukka Lehtosalo, PR [15472](https://github.com/python/mypy/pull/15472))
* mypyc: Fix classes with \_\_dict\_\_ on 3.12 (Jukka Lehtosalo, PR [15471](https://github.com/python/mypy/pull/15471))
* mypyc: Fix coroutines on Python 3.12 (Jukka Lehtosalo, PR [15469](https://github.com/python/mypy/pull/15469))
* mypyc: Don't use \_PyErr\_ChainExceptions on 3.12, since it's deprecated (Jukka Lehtosalo, PR [15468](https://github.com/python/mypy/pull/15468))
* mypyc: Add Python 3.12 feature macro (Jukka Lehtosalo, PR [15465](https://github.com/python/mypy/pull/15465))

Improvements to Dataclasses

* Improve signature of dataclasses.replace (Ilya Priven, PR [14849](https://github.com/python/mypy/pull/14849))
* Fix dataclass/protocol crash on joining types (Ilya Priven, PR [15629](https://github.com/python/mypy/pull/15629))
* Fix strict optional handling in dataclasses (Ivan Levkivskyi, PR [15571](https://github.com/python/mypy/pull/15571))
* Support optional types for custom dataclass descriptors (Marc Mueller, PR [15628](https://github.com/python/mypy/pull/15628))
* Add `__slots__` attribute to dataclasses (Nikita Sobolev, PR [15649](https://github.com/python/mypy/pull/15649))
* Support better \_\_post\_init\_\_ method signature for dataclasses (Nikita Sobolev, PR [15503](https://github.com/python/mypy/pull/15503))

Mypyc Improvements

* Support unsigned 8-bit native integer type: mypy\_extensions.u8 (Jukka Lehtosalo, PR [15564](https://github.com/python/mypy/pull/15564))
* Support signed 16-bit native integer type: mypy\_extensions.i16 (Jukka Lehtosalo, PR [15464](https://github.com/python/mypy/pull/15464))
* Define mypy\_extensions.i16 in stubs (Jukka Lehtosalo, PR [15562](https://github.com/python/mypy/pull/15562))
* Document more unsupported features and update supported features (Richard Si, PR [15524](https://github.com/python/mypy/pull/15524))
* Fix final NamedTuple classes (Richard Si, PR [15513](https://github.com/python/mypy/pull/15513))
* Use C99 compound literals for undefined tuple values (Jukka Lehtosalo, PR [15453](https://github.com/python/mypy/pull/15453))
* Don't explicitly assign NULL values in setup functions (Logan Hunt, PR [15379](https://github.com/python/mypy/pull/15379))

Stubgen Improvements

* Teach stubgen to work with complex and unary expressions (Nikita Sobolev, PR [15661](https://github.com/python/mypy/pull/15661))
* Support ParamSpec and TypeVarTuple (Ali Hamdan, PR [15626](https://github.com/python/mypy/pull/15626))
* Fix crash on non-str docstring (Ali Hamdan, PR [15623](https://github.com/python/mypy/pull/15623))

Documentation Updates

* Add documentation for additional error codes (Ivan Levkivskyi, PR [15539](https://github.com/python/mypy/pull/15539))
* Improve documentation of type narrowing (Ilya Priven, PR [15652](https://github.com/python/mypy/pull/15652))
* Small improvements to protocol documentation (Shantanu, PR [15460](https://github.com/python/mypy/pull/15460))
* Remove confusing instance variable example in cheat sheet (Adel Atallah, PR [15441](https://github.com/python/mypy/pull/15441))

Other Notable Fixes and Improvements

* Constant fold additional unary and binary expressions (Richard Si, PR [15202](https://github.com/python/mypy/pull/15202))
* Exclude the same special attributes from Protocol as CPython (Kyle Benesch, PR [15490](https://github.com/python/mypy/pull/15490))
* Change the default value of the slots argument of attrs.define to True, to match runtime behavior (Ilya Priven, PR [15642](https://github.com/python/mypy/pull/15642))
* Fix type of class attribute if attribute is defined in both class and metaclass (Alex Waygood, PR [14988](https://github.com/python/mypy/pull/14988))
* Handle type the same as typing.Type in the first argument of classmethods (Erik Kemperman, PR [15297](https://github.com/python/mypy/pull/15297))
* Fix \--find-occurrences flag (Shantanu, PR [15528](https://github.com/python/mypy/pull/15528))
* Fix error location for class patterns (Nikita Sobolev, PR [15506](https://github.com/python/mypy/pull/15506))
* Fix re-added file with errors in mypy daemon (Ivan Levkivskyi, PR [15440](https://github.com/python/mypy/pull/15440))
* Fix dmypy run on Windows (Ivan Levkivskyi, PR [15429](https://github.com/python/mypy/pull/15429))
* Fix abstract and non-abstract variant error for property deleter (Shantanu, PR [15395](https://github.com/python/mypy/pull/15395))
* Remove special casing for "cannot" in error messages (Ilya Priven, PR [15428](https://github.com/python/mypy/pull/15428))
* Add runtime `__slots__` attribute to attrs classes (Nikita Sobolev, PR [15651](https://github.com/python/mypy/pull/15651))
* Add get\_expression\_type to CheckerPluginInterface (Ilya Priven, PR [15369](https://github.com/python/mypy/pull/15369))
* Remove parameters that no longer exist from NamedTuple.\_make() (Alex Waygood, PR [15578](https://github.com/python/mypy/pull/15578))
* Allow using typing.Self in `__all__` with an explicit staticmethod decorator (Erik Kemperman, PR [15353](https://github.com/python/mypy/pull/15353))
* Fix self types in subclass methods without Self annotation (Ivan Levkivskyi, PR [15541](https://github.com/python/mypy/pull/15541))
* Check for abstract class objects in tuples (Nikita Sobolev, PR [15366](https://github.com/python/mypy/pull/15366))

Typeshed Updates

Typeshed is now modular and distributed as separate PyPI packages for everything except the standard library stubs. Please see [git log](https://github.com/python/typeshed/commits/main?after=fc7d4722eaa54803926cee5730e1f784979c0531+0&branch=main&path=stdlib) for full list of typeshed changes.

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

* Adel Atallah
* Alex Waygood
* Ali Hamdan
* Erik Kemperman
* Federico Padua
* Ilya Priven
* Ivan Levkivskyi
* Jelle Zijlstra
* Jared Hance
* Jukka Lehtosalo
* Kyle Benesch
* Logan Hunt
* Marc Mueller
* Nikita Sobolev
* Richard Si
* Shantanu
* Stavros Ntentos
* Valentin Stanciu

Posted by Valentin Stanciu