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This PR pins mypy to the latest release 1.18.1.

Changelog

1.18

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.

Type caching optimizations have a small risk of causing regressions. When
reporting issues with unexpected inferred types, please also check if
`--disable-expression-cache` will work around the issue, as it turns off some of
these optimizations.

- Improve self check performance by 1.8% (Jukka Lehtosalo, PR [19768](https://github.com/python/mypy/pull/19768), [19769](https://github.com/python/mypy/pull/19769), [19770](https://github.com/python/mypy/pull/19770))
- Optimize fixed-format deserialization (Ivan Levkivskyi, PR [19765](https://github.com/python/mypy/pull/19765))
- Use macros to optimize fixed-format deserialization (Ivan Levkivskyi, PR [19757](https://github.com/python/mypy/pull/19757))
- Two additional micro‑optimizations (Ivan Levkivskyi, PR [19627](https://github.com/python/mypy/pull/19627))
- Another set of micro‑optimizations (Ivan Levkivskyi, PR [19633](https://github.com/python/mypy/pull/19633))
- Cache common types (Ivan Levkivskyi, PR [19621](https://github.com/python/mypy/pull/19621))
- Skip more method bodies in third‑party libraries for speed (Ivan Levkivskyi, PR [19586](https://github.com/python/mypy/pull/19586))
- Simplify the representation of callable types (Ivan Levkivskyi, PR [19580](https://github.com/python/mypy/pull/19580))
- Add cache for types of some expressions (Ivan Levkivskyi, PR [19505](https://github.com/python/mypy/pull/19505))
- Use cache for dictionary expressions (Ivan Levkivskyi, PR [19536](https://github.com/python/mypy/pull/19536))
- Use cache for binary operations (Ivan Levkivskyi, PR [19523](https://github.com/python/mypy/pull/19523))
- Cache types of type objects (Ivan Levkivskyi, PR [19514](https://github.com/python/mypy/pull/19514))
- 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, PRs [19385](https://github.com/python/mypy/pull/19385) and [19462](https://github.com/python/mypy/pull/19462))
- Remove nested imports from the default plugin (Ivan Levkivskyi, PR [19388](https://github.com/python/mypy/pull/19388))
- Micro‑optimize type expansion (Jukka Lehtosalo, PR [19461](https://github.com/python/mypy/pull/19461))
- Micro‑optimize type indirection (Jukka Lehtosalo, PR [19460](https://github.com/python/mypy/pull/19460))
- Micro‑optimize the plugin framework (Jukka Lehtosalo, PR [19464](https://github.com/python/mypy/pull/19464))
- Avoid temporary set creation in subtype checking (Jukka Lehtosalo, PR [19463](https://github.com/python/mypy/pull/19463))
- Subtype checking micro‑optimization (Jukka Lehtosalo, PR [19384](https://github.com/python/mypy/pull/19384))
- Return early where possible in subtype check (Stanislav Terliakov, PR [19400](https://github.com/python/mypy/pull/19400))
- Deduplicate some types before joining (Stanislav Terliakov, PR [19409](https://github.com/python/mypy/pull/19409))
- Speed up type checking by caching argument inference context (Jukka Lehtosalo, PR [19323](https://github.com/python/mypy/pull/19323))
- Optimize binding method self argument type and deprecation checks (Ivan Levkivskyi, PR [19556](https://github.com/python/mypy/pull/19556))
- Keep trivial instance types/aliases during expansion (Ivan Levkivskyi, PR [19543](https://github.com/python/mypy/pull/19543))

Fixed‑Format Cache (Experimental)

Mypy now supports a new cache format used for faster incremental builds. It makes
incremental builds up to twice as fast. The feature is experimental and
currently only supported when using a compiled version of mypy. Use `--fixed-format-cache`
to enable the new format, or `fixed_format_cache = True` in a configuration file.

We plan to enable this by default in a future mypy release, and we'll eventually
deprecate and remove support for the original JSON-based format.

Unlike the JSON-based cache format, the new binary format is currently
not easy to parse and inspect by mypy users. We are planning to provide a tool to
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. (Using
`MypyFile.read(binary_data)` to inspect cache data may be sufficient to support
some use cases.)

This feature was contributed by Ivan Levkivskyi (PR [19668](https://github.com/python/mypy/pull/19668), [19735](https://github.com/python/mypy/pull/19735), [19750](https://github.com/python/mypy/pull/19750), [19681](https://github.com/python/mypy/pull/19681), [19752](https://github.com/python/mypy/pull/19752), [19815](https://github.com/python/mypy/pull/19815)).

Flexible Variable Definitions: Update

1.17.1

* Retain `None` as constraints bottom if no bottoms were provided (Stanislav Terliakov, PR [19485](https://github.com/python/mypy/pull/19485))
* Fix "ignored exception in `hasattr`" in dmypy (Stanislav Terliakov, PR [19428](https://github.com/python/mypy/pull/19428))
* Prevent a crash when InitVar is redefined with a method in a subclass (Stanislav Terliakov, PR [19453](https://github.com/python/mypy/pull/19453))

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

* Alexey Makridenko
* Brian Schubert
* Chad Dombrova
* Chainfire
* Charlie Denton
* Charulata
* Christoph Tyralla
* CoolCat467
* Donal Burns
* Guy Wilson
* Ivan Levkivskyi
* johnthagen
* Jukka Lehtosalo
* Łukasz Kwieciński
* Marc Mueller
* Michael J. Sullivan
* Mikhail Golubev
* Sebastian Rittau
* Shantanu
* Stanislav Terliakov
* wyattscarpenter

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

1.17

We’ve just uploaded mypy 1.17 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
Mypy is a static type checker for Python. This release includes new features 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).

Optionally Check That Match Is Exhaustive

Mypy can now optionally generate an error if a match statement does not
match exhaustively, without having to use `assert_never(...)`. Enable
this by using `--enable-error-code exhaustive-match`.

Example:

python
mypy: enable-error-code=exhaustive-match

import enum

class Color(enum.Enum):
 RED = 1
 BLUE = 2

def show_color(val: Color) -> None:
  error: Unhandled case for values of type "Literal[Color.BLUE]"
 match val:
     case Color.RED:
         print("red")


This feature was contributed by Donal Burns (PR [19144](https://github.com/python/mypy/pull/19144)).

Further Improvements to Attribute Resolution

This release includes additional improvements to how attribute types
and kinds are resolved. These fix many bugs and overall improve consistency.

* Handle corner case: protocol/class variable/descriptor (Ivan Levkivskyi, PR [19277](https://github.com/python/mypy/pull/19277))
* Fix a few inconsistencies in protocol/type object interactions (Ivan Levkivskyi, PR [19267](https://github.com/python/mypy/pull/19267))
* Refactor/unify access to static attributes (Ivan Levkivskyi, PR [19254](https://github.com/python/mypy/pull/19254))
* Remove inconsistencies in operator handling (Ivan Levkivskyi, PR [19250](https://github.com/python/mypy/pull/19250))
* Make protocol subtyping more consistent (Ivan Levkivskyi, PR [18943](https://github.com/python/mypy/pull/18943))

Fixes to Nondeterministic Type Checking

Previous mypy versions could infer different types for certain expressions
across different runs (typically depending on which order certain types
were processed, and this order was nondeterministic). This release includes
fixes to several such issues.

* Fix nondeterministic type checking by making join with explicit Protocol and type promotion commute (Shantanu, PR [18402](https://github.com/python/mypy/pull/18402))
* Fix nondeterministic type checking caused by nonassociative of None joins (Shantanu, PR [19158](https://github.com/python/mypy/pull/19158))
* Fix nondeterministic type checking caused by nonassociativity of joins (Shantanu, PR [19147](https://github.com/python/mypy/pull/19147))
* Fix nondeterministic type checking by making join between `type` and TypeVar commute (Shantanu, PR [19149](https://github.com/python/mypy/pull/19149))

Remove Support for Targeting Python 3.8

Mypy now requires `--python-version 3.9` or greater. Support for targeting Python 3.8 is
fully removed now. Since 3.8 is an unsupported version, mypy will default to the oldest
supported version (currently 3.9) if you still try to target 3.8.

This change is necessary because typeshed stopped supporting Python 3.8 after it
reached its End of Life in October 2024.

Contributed by Marc Mueller
(PR [19157](https://github.com/python/mypy/pull/19157), PR [19162](https://github.com/python/mypy/pull/19162)).

Initial Support for Python 3.14

Mypy is now tested on 3.14 and mypyc works with 3.14.0b3 and later.
Binary wheels compiled with mypyc for mypy itself will be available for 3.14
some time after 3.14.0rc1 has been released.

Note that not all features are supported just yet.

Contributed by Marc Mueller (PR [19164](https://github.com/python/mypy/pull/19164))

Deprecated Flag: `--force-uppercase-builtins`

Mypy only supports Python 3.9+. The `--force-uppercase-builtins` flag is now
deprecated as unnecessary, and a no-op. It will be removed in a future version.

Contributed by Marc Mueller (PR [19176](https://github.com/python/mypy/pull/19176))

Mypyc: Improvements to Generators and Async Functions

This release includes both performance improvements and bug fixes related
to generators and async functions (these share many implementation details).

* Fix exception swallowing in async try/finally blocks with await (Chainfire, PR [19353](https://github.com/python/mypy/pull/19353))
* Fix AttributeError in async try/finally with mixed return paths (Chainfire, PR [19361](https://github.com/python/mypy/pull/19361))
* Make generated generator helper method internal (Jukka Lehtosalo, PR [19268](https://github.com/python/mypy/pull/19268))
* Free coroutine after await encounters StopIteration (Jukka Lehtosalo, PR [19231](https://github.com/python/mypy/pull/19231))
* Use non-tagged integer for generator label (Jukka Lehtosalo, PR [19218](https://github.com/python/mypy/pull/19218))
* Merge generator and environment classes in simple cases (Jukka Lehtosalo, PR [19207](https://github.com/python/mypy/pull/19207))

Mypyc: Partial, Unsafe Support for Free Threading

Mypyc has minimal, quite memory-unsafe support for the free threaded
builds of 3.14. It is also only lightly tested. Bug reports and experience
reports are welcome!

Here are some of the major limitations:
* Free threading only works when compiling a single module at a time.
* If there is concurrent access to an object while another thread is mutating the same
object, it's possible to encounter segfaults and memory corruption.
* There are no efficient native primitives for thread synthronization, though the
regular `threading` module can be used.
* Some workloads don't scale well to multiple threads for no clear reason.

Related PRs:

* Enable partial, unsafe support for free-threading (Jukka Lehtosalo, PR [19167](https://github.com/python/mypy/pull/19167))
* Fix incref/decref on free-threaded builds (Jukka Lehtosalo, PR [19127](https://github.com/python/mypy/pull/19127))

Other Mypyc Fixes and Improvements

* Derive .c file name from full module name if using multi_file (Jukka Lehtosalo, PR [19278](https://github.com/python/mypy/pull/19278))
* Support overriding the group name used in output files (Jukka Lehtosalo, PR [19272](https://github.com/python/mypy/pull/19272))
* Add note about using non-native class to subclass built-in types (Jukka Lehtosalo, PR [19236](https://github.com/python/mypy/pull/19236))
* Make some generated classes implicitly final (Jukka Lehtosalo, PR [19235](https://github.com/python/mypy/pull/19235))
* Don't simplify module prefixes if using separate compilation (Jukka Lehtosalo, PR [19206](https://github.com/python/mypy/pull/19206))

Stubgen Improvements

* Add import for `types` in `__exit__` method signature (Alexey Makridenko, PR [19120](https://github.com/python/mypy/pull/19120))
* Add support for including class and property docstrings (Chad Dombrova, PR [17964](https://github.com/python/mypy/pull/17964))
* Don't generate `Incomplete | None = None` argument annotation (Sebastian Rittau, PR [19097](https://github.com/python/mypy/pull/19097))
* Support several more constructs in stubgen's alias printer (Stanislav Terliakov, PR [18888](https://github.com/python/mypy/pull/18888))

Miscellaneous Fixes and Improvements

* Combine the revealed types of multiple iteration steps in a more robust manner (Christoph Tyralla, PR [19324](https://github.com/python/mypy/pull/19324))
* Improve the handling of "iteration dependent" errors and notes in finally clauses (Christoph Tyralla, PR [19270](https://github.com/python/mypy/pull/19270))
* Lessen dmypy suggest path limitations for Windows machines (CoolCat467, PR [19337](https://github.com/python/mypy/pull/19337))
* Fix type ignore comments erroneously marked as unused by dmypy (Charlie Denton, PR [15043](https://github.com/python/mypy/pull/15043))
* Fix misspelled `exhaustive-match` error code (johnthagen, PR [19276](https://github.com/python/mypy/pull/19276))
* Fix missing error context for unpacking assignment involving star expression (Brian Schubert, PR [19258](https://github.com/python/mypy/pull/19258))
* Fix and simplify error de-duplication (Ivan Levkivskyi, PR [19247](https://github.com/python/mypy/pull/19247))
* Disallow `ClassVar` in type aliases (Brian Schubert, PR [19263](https://github.com/python/mypy/pull/19263))
* Add script that prints list of compiled files when compiling mypy (Jukka Lehtosalo, PR [19260](https://github.com/python/mypy/pull/19260))
* Fix help message url for "None and Optional handling" section (Guy Wilson, PR [19252](https://github.com/python/mypy/pull/19252))
* Display fully qualified name of imported base classes in errors about incompatible overrides (Mikhail Golubev, PR [19115](https://github.com/python/mypy/pull/19115))
* Avoid false `unreachable`, `redundant-expr`, and `redundant-casts` warnings in loops more robustly and efficiently, and avoid multiple `revealed type` notes for the same line (Christoph Tyralla, PR [19118](https://github.com/python/mypy/pull/19118))
* Fix type extraction from `isinstance` checks (Stanislav Terliakov, PR [19223](https://github.com/python/mypy/pull/19223))
* Erase stray type variables in `functools.partial` (Stanislav Terliakov, PR [18954](https://github.com/python/mypy/pull/18954))
* Make inferring condition value recognize the whole truth table (Stanislav Terliakov, PR [18944](https://github.com/python/mypy/pull/18944))
* Support type aliases, `NamedTuple` and `TypedDict` in constrained TypeVar defaults (Stanislav Terliakov, PR [18884](https://github.com/python/mypy/pull/18884))
* Move dataclass `kw_only` fields to the end of the signature (Stanislav Terliakov, PR [19018](https://github.com/python/mypy/pull/19018))
* Provide a better fallback value for the `python_version` option (Marc Mueller, PR [19162](https://github.com/python/mypy/pull/19162))
* Avoid spurious non-overlapping equality error with metaclass with `__eq__` (Michael J. Sullivan, PR [19220](https://github.com/python/mypy/pull/19220))
* Narrow type variable bounds (Ivan Levkivskyi, PR [19183](https://github.com/python/mypy/pull/19183))
* Add classifier for Python 3.14 (Marc Mueller, PR [19199](https://github.com/python/mypy/pull/19199))
* Capitalize syntax error messages (Charulata, PR [19114](https://github.com/python/mypy/pull/19114))
* Infer constraints eagerly if actual is Any (Ivan Levkivskyi, PR [19190](https://github.com/python/mypy/pull/19190))
* Include walrus assignments in conditional inference (Stanislav Terliakov, PR [19038](https://github.com/python/mypy/pull/19038))
* Use PEP 604 syntax when converting types to strings (Marc Mueller, PR [19179](https://github.com/python/mypy/pull/19179))
* Use more lower-case builtin types in error messages (Marc Mueller, PR [19177](https://github.com/python/mypy/pull/19177))
* Fix example to use correct method of Stack (Łukasz Kwieciński, PR [19123](https://github.com/python/mypy/pull/19123))
* Forbid `.pop` of `Readonly` `NotRequired` TypedDict items (Stanislav Terliakov, PR [19133](https://github.com/python/mypy/pull/19133))
* Emit a friendlier warning on invalid exclude regex, instead of a stacktrace (wyattscarpenter, PR [19102](https://github.com/python/mypy/pull/19102))
* Enable ANSI color codes for dmypy client in Windows (wyattscarpenter, PR [19088](https://github.com/python/mypy/pull/19088))
* Extend special case for context-based type variable inference to unions in return position (Stanislav Terliakov, PR [18976](https://github.com/python/mypy/pull/18976))

1.16

We’ve just uploaded mypy 1.16 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
Mypy is a static type checker for Python. This release includes new features 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).

Different Property Getter and Setter Types

Mypy now supports using different types for a property getter and setter:

python
class A:
 _value: int

 property
 def foo(self) -> int:
     return self._value

 foo.setter
 def foo(self, x: str | int) -> None:
     try:
         self._value = int(x)
     except ValueError:
         raise Exception(f"'{x}' is not a valid value for 'foo'")

This was contributed by Ivan Levkivskyi (PR [18510](https://github.com/python/mypy/pull/18510)).

Flexible Variable Redefinitions (Experimental)

Mypy now allows unannotated variables to be freely redefined with
different types when using the experimental `--allow-redefinition-new`
flag. You will also need to enable `--local-partial-types`. Mypy will
now infer a union type when different types are assigned to a
variable:

py
mypy: allow-redefinition-new, local-partial-types

def f(n: int, b: bool) -> int | str:
 if b:
     x = n
 else:
     x = str(n)
  Type of 'x' is int | str here.
 return x


Without the new flag, mypy only supports inferring optional types (`X
| None`) from multiple assignments, but now mypy can infer arbitrary
union types.

An unannotated variable can now also have different types in different
code locations:

py
mypy: allow-redefinition-new, local-partial-types
...

if cond():
 for x in range(n):
      Type of 'x' is 'int' here
     ...
else:
 for x in ['a', 'b']:
      Type of 'x' is 'str' here
     ...


We are planning to turn this flag on by default in mypy 2.0, along
with `--local-partial-types`. The feature is still experimental and
has known issues, and the semantics may still change in the
future. You may need to update or add type annotations when switching
to the new behavior, but if you encounter anything unexpected, please
create a GitHub issue.

This was contributed by Jukka Lehtosalo
(PR [18727](https://github.com/python/mypy/pull/18727), PR [19153](https://github.com/python/mypy/pull/19153)).

Stricter Type Checking with Imprecise Types

Mypy can now detect additional errors in code that uses `Any` types or has missing function annotations.

When calling `dict.get(x, None)` on an object of type `dict[str, Any]`, this
now results in an optional type (in the past it was `Any`):

python
def f(d: dict[str, Any]) -> int:
  Error: Return value has type "Any | None" but expected "int"
 return d.get("x", None)


Type narrowing using assignments can result in more precise types in
the presence of `Any` types:

python
def foo(): ...

def bar(n: int) -> None:
 x = foo()
  Type of 'x' is 'Any' here
 if n > 5:
     x = str(n)
      Type of 'x' is 'str' here


When using `--check-untyped-defs`, unannotated overrides are now
checked more strictly against superclass definitions.

Related PRs:

* Use union types instead of join in binder (Ivan Levkivskyi, PR [18538](https://github.com/python/mypy/pull/18538))
* Check superclass compatibility of untyped methods if `--check-untyped-defs` is set (Stanislav Terliakov, PR [18970](https://github.com/python/mypy/pull/18970))

Improvements to Attribute Resolution

This release includes several fixes to inconsistent resolution of attribute, method and descriptor types.

* Consolidate descriptor handling (Ivan Levkivskyi, PR [18831](https://github.com/python/mypy/pull/18831))
* Make multiple inheritance checking use common semantics (Ivan Levkivskyi, PR [18876](https://github.com/python/mypy/pull/18876))
* Make method override checking use common semantics  (Ivan Levkivskyi, PR [18870](https://github.com/python/mypy/pull/18870))
* Fix descriptor overload selection (Ivan Levkivskyi, PR [18868](https://github.com/python/mypy/pull/18868))
* Handle union types when binding `self` (Ivan Levkivskyi, PR [18867](https://github.com/python/mypy/pull/18867))
* Make variable override checking use common semantics (Ivan Levkivskyi, PR [18847](https://github.com/python/mypy/pull/18847))
* Make descriptor handling behave consistently (Ivan Levkivskyi, PR [18831](https://github.com/python/mypy/pull/18831))

Make Implementation for Abstract Overloads Optional

The implementation can now be omitted for abstract overloaded methods,
even outside stubs:

py
from abc import abstractmethod
from typing import overload

class C:
 abstractmethod
 overload
 def foo(self, x: int) -> int: ...

 abstractmethod
 overload
 def foo(self, x: str) -> str: ...

  No implementation required for "foo"


This was contributed by Ivan Levkivskyi (PR [18882](https://github.com/python/mypy/pull/18882)).

Option to Exclude Everything in .gitignore

You can now use `--exclude-gitignore` to exclude everything in a
`.gitignore` file from the mypy build. This behaves similar to
excluding the paths using `--exclude`. We might enable this by default
in a future mypy release.

This was contributed by Ivan Levkivskyi (PR [18696](https://github.com/python/mypy/pull/18696)).

Selectively Disable Deprecated Warnings

It's now possible to selectively disable warnings generated from
[`warnings.deprecated`](https://docs.python.org/3/library/warnings.html#warnings.deprecated)
using the [`--deprecated-calls-exclude`](https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-deprecated-calls-exclude)
option:

python
mypy --enable-error-code deprecated
   --deprecated-calls-exclude=foo.A
import foo

foo.A().func()   OK, the deprecated warning is ignored


python
file foo.py

from typing_extensions import deprecated

class A:
 deprecated("Use A.func2 instead")
 def func(self): pass

 ...


Contributed by Marc Mueller (PR [18641](https://github.com/python/mypy/pull/18641))

Annotating Native/Non-Native Classes in Mypyc

You can now declare a class as a non-native class when compiling with
mypyc. Unlike native classes, which are extension classes and have an
immutable structure, non-native classes are normal Python classes at
runtime and are fully dynamic.  Example:

python
from mypy_extensions import mypyc_attr

mypyc_attr(native_class=False)
class NonNativeClass:
 ...

o = NonNativeClass()

Ok, even if attribute "foo" not declared in class body
setattr(o, "foo", 1)


Classes are native by default in compiled modules, but classes that
use certain features (such as most metaclasses) are implicitly
non-native.

You can also explicitly declare a class as native. In this case mypyc
will generate an error if it can't compile the class as a native
class, instead of falling back to a non-native class:

python
from mypy_extensions import mypyc_attr
from foo import MyMeta

Error: Unsupported metaclass for a native class
mypyc_attr(native_class=True)
class C(metaclass=MyMeta):
 ...


Since native classes are significantly more efficient that non-native
classes, you may want to ensure that certain classes always compiled
as native classes.

This feature was contributed by Valentin Stanciu (PR [18802](https://github.com/python/mypy/pull/18802)).

Mypyc Fixes and Improvements

* Improve documentation of native and non-native classes (Jukka Lehtosalo, PR [19154](https://github.com/python/mypy/pull/19154))
* Fix compilation when using Python 3.13 debug build (Valentin Stanciu, PR [19045](https://github.com/python/mypy/pull/19045))
* Show the reason why a class can't be a native class (Valentin Stanciu, PR [19016](https://github.com/python/mypy/pull/19016))
* Support await/yield while temporary values are live (Michael J. Sullivan, PR [16305](https://github.com/python/mypy/pull/16305))
* Fix spilling values with overlapping error values (Jukka Lehtosalo, PR [18961](https://github.com/python/mypy/pull/18961))
* Fix reference count of spilled register in async def (Jukka Lehtosalo, PR [18957](https://github.com/python/mypy/pull/18957))
* Add basic optimization for `sorted` (Marc Mueller, PR [18902](https://github.com/python/mypy/pull/18902))
* Fix access of class object in a type annotation (Advait Dixit, PR [18874](https://github.com/python/mypy/pull/18874))
* Optimize `list.__imul__` and `tuple.__mul__ `(Marc Mueller, PR [18887](https://github.com/python/mypy/pull/18887))
* Optimize `list.__add__`, `list.__iadd__` and `tuple.__add__` (Marc Mueller, PR [18845](https://github.com/python/mypy/pull/18845))
* Add and implement primitive `list.copy()` (exertustfm, PR [18771](https://github.com/python/mypy/pull/18771))
* Optimize `builtins.repr` (Marc Mueller, PR [18844](https://github.com/python/mypy/pull/18844))
* Support iterating over keys/values/items of dict-bound TypeVar and ParamSpec.kwargs (Stanislav Terliakov, PR [18789](https://github.com/python/mypy/pull/18789))
* Add efficient primitives for `str.strip()` etc. (Advait Dixit, PR [18742](https://github.com/python/mypy/pull/18742))
* Document that `strip()` etc. are optimized (Jukka Lehtosalo, PR [18793](https://github.com/python/mypy/pull/18793))
* Fix mypyc crash with enum type aliases (Valentin Stanciu, PR [18725](https://github.com/python/mypy/pull/18725))
* Optimize `str.find` and `str.rfind` (Marc Mueller, PR [18709](https://github.com/python/mypy/pull/18709))
* Optimize `str.__contains__` (Marc Mueller, PR [18705](https://github.com/python/mypy/pull/18705))
* Fix order of steal/unborrow in tuple unpacking (Ivan Levkivskyi, PR [18732](https://github.com/python/mypy/pull/18732))
* Optimize `str.partition` and `str.rpartition` (Marc Mueller, PR [18702](https://github.com/python/mypy/pull/18702))
* Optimize `str.startswith` and `str.endswith` with tuple argument (Marc Mueller, PR [18678](https://github.com/python/mypy/pull/18678))
* Improve `str.startswith` and `str.endswith` with tuple argument (Marc Mueller, PR [18703](https://github.com/python/mypy/pull/18703))
* `pythoncapi_compat`: don't define Py_NULL if it is already defined (Michael R. Crusoe, PR [18699](https://github.com/python/mypy/pull/18699))
* Optimize `str.splitlines` (Marc Mueller, PR [18677](https://github.com/python/mypy/pull/18677))
* Mark `dict.setdefault` as optimized (Marc Mueller, PR [18685](https://github.com/python/mypy/pull/18685))
* Support `__del__` methods (Advait Dixit, PR [18519](https://github.com/python/mypy/pull/18519))
* Optimize `str.rsplit` (Marc Mueller, PR [18673](https://github.com/python/mypy/pull/18673))
* Optimize `str.removeprefix` and `str.removesuffix` (Marc Mueller, PR [18672](https://github.com/python/mypy/pull/18672))
* Recognize literal types in `__match_args__` (Stanislav Terliakov, PR [18636](https://github.com/python/mypy/pull/18636))
* Fix non extension classes with attribute annotations using forward references (Valentin Stanciu, PR [18577](https://github.com/python/mypy/pull/18577))
* Use lower-case generic types such as `list[t]` in documentation (Jukka Lehtosalo, PR [18576](https://github.com/python/mypy/pull/18576))
* Improve support for `frozenset` (Marc Mueller, PR [18571](https://github.com/python/mypy/pull/18571))
* Fix wheel build for cp313-win (Marc Mueller, PR [18560](https://github.com/python/mypy/pull/18560))
* Reduce impact of immortality (introduced in Python 3.12) on reference counting performance (Jukka Lehtosalo, PR [18459](https://github.com/python/mypy/pull/18459))
* Update math error messages for 3.14 (Marc Mueller, PR [18534](https://github.com/python/mypy/pull/18534))
* Update math error messages for 3.14 (2) (Marc Mueller, PR [18949](https://github.com/python/mypy/pull/18949))
* Replace deprecated `_PyLong_new` with `PyLongWriter` API (Marc Mueller, PR [18532](https://github.com/python/mypy/pull/18532))

Fixes to Crashes

* Traverse module ancestors when traversing reachable graph nodes during dmypy update (Stanislav Terliakov, PR [18906](https://github.com/python/mypy/pull/18906))
* Fix crash on multiple unpacks in a bare type application (Stanislav Terliakov, PR [18857](https://github.com/python/mypy/pull/18857))
* Prevent crash when enum/TypedDict call is stored as a class attribute (Stanislav Terliakov, PR [18861](https://github.com/python/mypy/pull/18861))
* Fix crash on multiple unpacks in a bare type application (Stanislav Terliakov, PR [18857](https://github.com/python/mypy/pull/18857))
* Fix crash on type inference against non-normal callables (Ivan Levkivskyi, PR [18858](https://github.com/python/mypy/pull/18858))
* Fix crash on decorated getter in settable property (Ivan Levkivskyi, PR [18787](https://github.com/python/mypy/pull/18787))
* Fix crash on callable with `*args` and suffix against Any (Ivan Levkivskyi, PR [18781](https://github.com/python/mypy/pull/18781))
* Fix crash on deferred supertype and setter override (Ivan Levkivskyi, PR [18649](https://github.com/python/mypy/pull/18649))
* Fix crashes on incorrectly detected recursive aliases (Ivan Levkivskyi, PR [18625](https://github.com/python/mypy/pull/18625))
* Report that `NamedTuple` and `dataclass` are incompatile instead of crashing (Christoph Tyralla, PR [18633](https://github.com/python/mypy/pull/18633))
* Fix mypy daemon crash (Valentin Stanciu, PR [19087](https://github.com/python/mypy/pull/19087))

Performance Improvements

These are specific to mypy. Mypyc-related performance improvements are discussed elsewhere.

* Speed up binding `self` in trivial cases (Ivan Levkivskyi, PR [19024](https://github.com/python/mypy/pull/19024))
* Small constraint solver optimization (Aaron Gokaslan, PR [18688](https://github.com/python/mypy/pull/18688))

Documentation Updates

* Improve documentation of `--strict` (lenayoung8, PR [18903](https://github.com/python/mypy/pull/18903))
* Remove a note about `from __future__ import annotations` (Ageev Maxim, PR [18915](https://github.com/python/mypy/pull/18915))
* Improve documentation on type narrowing (Tim Hoffmann, PR [18767](https://github.com/python/mypy/pull/18767))
* Fix metaclass usage example (Georg, PR [18686](https://github.com/python/mypy/pull/18686))
* Update documentation on `extra_checks` flag (Ivan Levkivskyi, PR [18537](https://github.com/python/mypy/pull/18537))

Stubgen Improvements

* Fix `TypeAlias` handling (Alexey Makridenko, PR [18960](https://github.com/python/mypy/pull/18960))
* Handle `arg=None` in C extension modules (Anthony Sottile, PR [18768](https://github.com/python/mypy/pull/18768))
* Fix valid type detection to allow pipe unions (Chad Dombrova, PR [18726](https://github.com/python/mypy/pull/18726))
* Include simple decorators in stub files (Marc Mueller, PR [18489](https://github.com/python/mypy/pull/18489))
* Support positional and keyword-only arguments in stubdoc (Paul Ganssle, PR [18762](https://github.com/python/mypy/pull/18762))
* Fall back to `Incomplete` if we are unable to determine the module name (Stanislav Terliakov, PR [19084](https://github.com/python/mypy/pull/19084))

Stubtest Improvements

* Make stubtest ignore `__slotnames__` (Nick Pope, PR [19077](https://github.com/python/mypy/pull/19077))
* Fix stubtest tests on 3.14 (Jelle Zijlstra, PR [19074](https://github.com/python/mypy/pull/19074))
* Support for `strict_bytes` in stubtest (Joren Hammudoglu, PR [19002](https://github.com/python/mypy/pull/19002))
* Understand override (Shantanu, PR [18815](https://github.com/python/mypy/pull/18815))
* Better checking of runtime arguments with dunder names (Shantanu, PR [18756](https://github.com/python/mypy/pull/18756))
* Ignore setattr and delattr inherited from object (Stephen Morton, PR [18325](https://github.com/python/mypy/pull/18325))

Miscellaneous Fixes and Improvements

* Add `--strict-bytes` to `--strict` (wyattscarpenter, PR [19049](https://github.com/python/mypy/pull/19049))
* Admit that Final variables are never redefined (Stanislav Terliakov, PR [19083](https://github.com/python/mypy/pull/19083))
* Add special support for `django.cached_property` needed in `django-stubs` (sobolevn, PR [18959](https://github.com/python/mypy/pull/18959))
* Do not narrow types to `Never` with binder (Ivan Levkivskyi, PR [18972](https://github.com/python/mypy/pull/18972))
* Local forward references should precede global forward references (Ivan Levkivskyi, PR [19000](https://github.com/python/mypy/pull/19000))
* Do not cache module lookup results in incremental mode that may become invalid (Stanislav Terliakov, PR [19044](https://github.com/python/mypy/pull/19044))
* Only consider meta variables in ambiguous "any of" constraints (Stanislav Terliakov, PR [18986](https://github.com/python/mypy/pull/18986))
* Allow accessing `__init__` on final classes and when `__init__` is final (Stanislav Terliakov, PR [19035](https://github.com/python/mypy/pull/19035))
* Treat varargs as positional-only (A5rocks, PR [19022](https://github.com/python/mypy/pull/19022))
* Enable colored output for argparse help in Python 3.14 (Marc Mueller, PR [19021](https://github.com/python/mypy/pull/19021))
* Fix argparse for Python 3.14 (Marc Mueller, PR [19020](https://github.com/python/mypy/pull/19020))
* `dmypy suggest` can now suggest through contextmanager-based decorators (Anthony Sottile, PR [18948](https://github.com/python/mypy/pull/18948))
* Fix `__r<magic_methods>__` being used under the same `__<magic_method>__` hook (Arnav Jain, PR [18995](https://github.com/python/mypy/pull/18995))
* Prioritize `.pyi` from `-stubs` packages over bundled `.pyi` (Joren Hammudoglu, PR [19001](https://github.com/python/mypy/pull/19001))
* Fix missing subtype check case for `type[T]` (Stanislav Terliakov, PR [18975](https://github.com/python/mypy/pull/18975))
* Fixes to the detection of redundant casts (Anthony Sottile, PR [18588](https://github.com/python/mypy/pull/18588))
* Make some parse errors non-blocking (Shantanu, PR [18941](https://github.com/python/mypy/pull/18941))
* Fix PEP 695 type alias with a mix of type arguments (PEP 696) (Marc Mueller, PR [18919](https://github.com/python/mypy/pull/18919))
* Allow deeper recursion in mypy daemon, better error reporting (Carter Dodd, PR [17707](https://github.com/python/mypy/pull/17707))
* Fix swapped errors for frozen/non-frozen dataclass inheritance (Nazrawi Demeke, PR [18918](https://github.com/python/mypy/pull/18918))
* Fix incremental issue with namespace packages (Shantanu, PR [18907](https://github.com/python/mypy/pull/18907))
* Exclude irrelevant members when narrowing union overlapping with enum (Stanislav Terliakov, PR [18897](https://github.com/python/mypy/pull/18897))
* Flatten union before contracting literals when checking subtyping (Stanislav Terliakov, PR [18898](https://github.com/python/mypy/pull/18898))
* Do not add `kw_only` dataclass fields to `__match_args__` (sobolevn, PR [18892](https://github.com/python/mypy/pull/18892))
* Fix error message when returning long tuple with type mismatch (Thomas Mattone, PR [18881](https://github.com/python/mypy/pull/18881))
* Treat `TypedDict` (old-style) aliases as regular `TypedDict`s (Stanislav Terliakov, PR [18852](https://github.com/python/mypy/pull/18852))
* Warn about unused `type: ignore` comments when error code is disabled (Brian Schubert, PR [18849](https://github.com/python/mypy/pull/18849))
* Reject duplicate `ParamSpec.{args,kwargs}` at call site (Stanislav Terliakov, PR [18854](https://github.com/python/mypy/pull/18854))
* Make detection of enum members more consistent (sobolevn, PR [18675](https://github.com/python/mypy/pull/18675))
* Admit that `**kwargs` mapping subtypes may have no direct type parameters (Stanislav Terliakov, PR [18850](https://github.com/python/mypy/pull/18850))
* Don't suggest `types-setuptools` for `pkg_resources` (Shantanu, PR [18840](https://github.com/python/mypy/pull/18840))
* Suggest `scipy-stubs` for `scipy` as non-typeshed stub package (Joren Hammudoglu, PR [18832](https://github.com/python/mypy/pull/18832))
* Narrow tagged unions in match statements (Gene Parmesan Thomas, PR [18791](https://github.com/python/mypy/pull/18791))
* Consistently store settable property type (Ivan Levkivskyi, PR [18774](https://github.com/python/mypy/pull/18774))
* Do not blindly undefer on leaving function (Ivan Levkivskyi, PR [18674](https://github.com/python/mypy/pull/18674))
* Process superclass methods before subclass methods in semanal (Ivan Levkivskyi, PR [18723](https://github.com/python/mypy/pull/18723))
* Only defer top-level functions (Ivan Levkivskyi, PR [18718](https://github.com/python/mypy/pull/18718))
* Add one more type-checking pass (Ivan Levkivskyi, PR [18717](https://github.com/python/mypy/pull/18717))
* Properly account for `member` and `nonmember` in enums (sobolevn, PR [18559](https://github.com/python/mypy/pull/18559))
* Fix instance vs tuple subtyping edge case (Ivan Levkivskyi, PR [18664](https://github.com/python/mypy/pull/18664))
* Improve handling of Any/object in variadic generics (Ivan Levkivskyi, PR [18643](https://github.com/python/mypy/pull/18643))
* Fix handling of named tuples in class match pattern (Ivan Levkivskyi, PR [18663](https://github.com/python/mypy/pull/18663))
* Fix regression for user config files (Shantanu, PR [18656](https://github.com/python/mypy/pull/18656))
* Fix dmypy socket issue on GNU/Hurd (Mattias Ellert, PR [18630](https://github.com/python/mypy/pull/18630))
* Don't assume that for loop body index variable is always set (Jukka Lehtosalo, PR [18631](https://github.com/python/mypy/pull/18631))
* Fix overlap check for variadic generics (Ivan Levkivskyi, PR [18638](https://github.com/python/mypy/pull/18638))
* Improve support for `functools.partial` of overloaded callable protocol (Shantanu, PR [18639](https://github.com/python/mypy/pull/18639))
* Allow lambdas in `except*` clauses (Stanislav Terliakov, PR [18620](https://github.com/python/mypy/pull/18620))
* Fix trailing commas in many multiline string options in `pyproject.toml` (sobolevn, PR [18624](https://github.com/python/mypy/pull/18624))
* Allow trailing commas for `files` setting in `mypy.ini` and `setup.ini` (sobolevn, PR [18621](https://github.com/python/mypy/pull/18621))
* Fix "not callable" issue for `dataclass(frozen=True)` with `Final` attr (sobolevn, PR [18572](https://github.com/python/mypy/pull/18572))
* Add missing TypedDict special case when checking member access (Stanislav Terliakov, PR [18604](https://github.com/python/mypy/pull/18604))
* Use lower case `list` and `dict` in invariance notes (Jukka Lehtosalo, PR [18594](https://github.com/python/mypy/pull/18594))
* Fix inference when class and instance match protocol (Ivan Levkivskyi, PR [18587](https://github.com/python/mypy/pull/18587))
* Remove support for `builtins.Any` (Marc Mueller, PR [18578](https://github.com/python/mypy/pull/18578))
* Update the overlapping check for tuples to account for NamedTuples (A5rocks, PR [18564](https://github.com/python/mypy/pull/18564))
* Fix `deprecated` (PEP 702) with normal overloaded methods (Christoph Tyralla, PR [18477](https://github.com/python/mypy/pull/18477))
* Start propagating end columns/lines for `type-arg` errors (A5rocks, PR [18533](https://github.com/python/mypy/pull/18533))
* Improve handling of `type(x) is Foo` checks (Stanislav Terliakov, PR [18486](https://github.com/python/mypy/pull/18486))
* Suggest `typing.Literal` for exit-return error messages (Marc Mueller, PR [18541](https://github.com/python/mypy/pull/18541))
* Allow redefinitions in except/else/finally (Stanislav Terliakov, PR [18515](https://github.com/python/mypy/pull/18515))
* Disallow setting Python version using inline config (Shantanu, PR [18497](https://github.com/python/mypy/pull/18497))
* Improve type inference in tuple multiplication plugin (Shantanu, PR [18521](https://github.com/python/mypy/pull/18521))
* Add missing line number to `yield from` with wrong type (Stanislav Terliakov, PR [18518](https://github.com/python/mypy/pull/18518))
* Hint at argument names when formatting callables with compatible return types in error messages (Stanislav Terliakov, PR [18495](https://github.com/python/mypy/pull/18495))
* Add better naming and improve compatibility for ad hoc intersections of instances (Christoph Tyralla, PR [18506](https://github.com/python/mypy/pull/18506))

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

- A5rocks
- Aaron Gokaslan
- Advait Dixit
- Ageev Maxim
- Alexey Makridenko
- Ali Hamdan
- Anthony Sottile
- Arnav Jain
- Brian Schubert
- bzoracler
- Carter Dodd
- Chad Dombrova
- Christoph Tyralla
- Dimitri Papadopoulos Orfanos
- Emma Smith
- exertustfm
- Gene Parmesan Thomas
- Georg
- Ivan Levkivskyi
- Jared Hance
- Jelle Zijlstra
- Joren Hammudoglu
- lenayoung8
- Marc Mueller
- Mattias Ellert
- Michael J. Sullivan
- Michael R. Crusoe
- Nazrawi Demeke
- Nick Pope
- Paul Ganssle
- Shantanu
- sobolevn
- Stanislav Terliakov
- Stephen Morton
- Thomas Mattone
- Tim Hoffmann
- Tim Ruffing
- Valentin Stanciu
- Wesley Collin Wright
- wyattscarpenter

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

1.16.0

with different types, and inferring union types for variables from multiple assignments.
The feature is now documented in the `--help` output, but the feature is still experimental.

We are planning to enable this by default in mypy 2.0, and we will also deprecate the
older `--allow-redefinition` flag. Since the new behavior differs significantly from
the older flag, we encourage users of `--allow-redefinition` to experiment with
`--allow-redefinition-new` and create a GitHub issue if the new functionality doesn't
support some important use cases.

This feature was contributed by Jukka Lehtosalo.

Inferred Type for Bare ClassVar

A ClassVar without an explicit type annotation now causes the type of the variable
to be inferred from the initializer:


python
from typing import ClassVar

class Item:
  Type of 'next_id' is now 'int' (it was 'Any')
 next_id: ClassVar = 1

 ...


This feature was contributed by Ivan Levkivskyi (PR [19573](https://github.com/python/mypy/pull/19573)).

Disjoint Base Classes (disjoint_base, PEP 800)

Mypy now understands disjoint bases (PEP 800): it recognizes the `disjoint_base`
decorator, and rejects class definitions that combine mutually incompatible base classes,
and takes advantage of the fact that such classes cannot exist in reachability and
narrowing logic.

This class definition will now generate an error:

python
Error: Class "Bad" has incompatible disjoint bases
class Bad(str, Exception):
 ...


This feature was contributed by Jelle Zijlstra (PR [19678](https://github.com/python/mypy/pull/19678)).

Miscellaneous New Mypy Features

- 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 such as `assert sys.platform == "linux"` that is always false (Stanislav Terliakov, PR [19347](https://github.com/python/mypy/pull/19347))

Improvements to Match Statements

- Add temporary named expressions for match subjects (Stanislav Terliakov, PR [18446](https://github.com/python/mypy/pull/18446))
- Fix unwrapping of assignment expressions in match subject (Marc Mueller, PR [19742](https://github.com/python/mypy/pull/19742))
- Omit errors for class patterns against object (Marc Mueller, PR [19709](https://github.com/python/mypy/pull/19709))
- Remove unnecessary error for certain match class patterns (Marc Mueller, PR [19708](https://github.com/python/mypy/pull/19708))
- Use union type for captured vars in or pattern (Marc Mueller, PR [19710](https://github.com/python/mypy/pull/19710))
- Prevent final reassignment inside match case (Omer Hadari, PR [19496](https://github.com/python/mypy/pull/19496))

Fixes to Crashes

- Fix crash with variadic tuple arguments to a generic type (Randolf Scholz, PR [19705](https://github.com/python/mypy/pull/19705))
- Fix crash when enable_error_code in pyproject.toml has wrong type (wyattscarpenter, PR [19494](https://github.com/python/mypy/pull/19494))
- Prevent crash for dataclass with PEP 695 TypeVarTuple on Python 3.13+ (Stanislav Terliakov, PR [19565](https://github.com/python/mypy/pull/19565))
- Fix crash on settable property alias (Ivan Levkivskyi, PR [19615](https://github.com/python/mypy/pull/19615))

Experimental Free-threading Support for Mypyc

All mypyc tests now pass on free-threading Python 3.14 release candidate builds. The performance
of various micro-benchmarks scale well across multiple threads.

Free-threading support is still experimental. Note that native attribute access
(get and set), list item access and certain other operations are still
unsafe when there are race conditions. This will likely change in the future.
You can follow the
[area-free-threading label](https://github.com/mypyc/mypyc/issues?q=is%3Aissue%20state%3Aopen%20label%3Aarea-free-threading)
in the mypyc issues tracker to follow progress.

Related PRs:
- Enable free‑threading when compiling multiple modules (Jukka Lehtosalo, PR [19541](https://github.com/python/mypy/pull/19541))
- Fix `list.pop` on free‑threaded builds (Jukka Lehtosalo, PR [19522](https://github.com/python/mypy/pull/19522))
- Make type objects immortal under free‑threading (Jukka Lehtosalo, PR [19538](https://github.com/python/mypy/pull/19538))

Mypyc: Support `__new__`

Mypyc now has rudimentary support for user-defined `__new__` methods.

This feature was contributed by Piotr Sawicki (PR [19739](https://github.com/python/mypy/pull/19739)).

Mypyc: Faster Generators and Async Functions

Generators and calls of async functions are now faster, sometimes by 2x or more.

Related PRs:
- Speed up for loops over native generators (Jukka Lehtosalo, PR [19415](https://github.com/python/mypy/pull/19415))
- Speed up native‑to‑native calls using await (Jukka Lehtosalo, PR [19398](https://github.com/python/mypy/pull/19398))
- Call generator helper directly in await expressions (Jukka Lehtosalo, PR [19376](https://github.com/python/mypy/pull/19376))
- Speed up generator allocation with per‑type freelists (Jukka Lehtosalo, PR [19316](https://github.com/python/mypy/pull/19316))

Miscellaneous Mypyc Improvements

- Special‑case certain Enum method calls for speed (Ivan Levkivskyi, PR [19634](https://github.com/python/mypy/pull/19634))
- Fix issues related to subclassing and undefined attribute tracking (Chainfire, PR [19787](https://github.com/python/mypy/pull/19787))
- Fix invalid C function signature (Jukka Lehtosalo, PR [19773](https://github.com/python/mypy/pull/19773))
- Speed up implicit `__ne__` (Jukka Lehtosalo, PR [19759](https://github.com/python/mypy/pull/19759))
- Speed up equality with optional str/bytes types (Jukka Lehtosalo, PR [19758](https://github.com/python/mypy/pull/19758))
- Speed up access to empty tuples (BobTheBuidler, PR [19654](https://github.com/python/mypy/pull/19654))
- Speed up calls with `*args` (BobTheBuidler, PRs [19623](https://github.com/python/mypy/pull/19623) and [19631](https://github.com/python/mypy/pull/19631))
- Speed up calls with `**kwargs` (BobTheBuidler, PR [19630](https://github.com/python/mypy/pull/19630))
- Optimize `type(x)`, `x.__class__`, and `<type>.__name__` (Jukka Lehtosalo, PR [19691](https://github.com/python/mypy/pull/19691), [19683](https://github.com/python/mypy/pull/19683))
- Specialize `bytes.decode` for common encodings (Jukka Lehtosalo, PR [19688](https://github.com/python/mypy/pull/19688))
- Speed up `in` operations using final fixed‑length tuples (Jukka Lehtosalo, PR [19682](https://github.com/python/mypy/pull/19682))
- Optimize f‑string building from final values (BobTheBuidler, PR [19611](https://github.com/python/mypy/pull/19611))
- Add dictionary set item for exact dict instances (BobTheBuidler, PR [19657](https://github.com/python/mypy/pull/19657))
- Cache length when iterating over immutable types (BobTheBuidler, PR [19656](https://github.com/python/mypy/pull/19656))
- Fix name conflict related to attributes of generator classes (Piotr Sawicki, PR [19535](https://github.com/python/mypy/pull/19535))
- Fix segfault from heap type objects with a static docstring (Brian Schubert, PR [19636](https://github.com/python/mypy/pull/19636))
- Unwrap NewType to its base type for additional optimizations (BobTheBuidler, PR [19497](https://github.com/python/mypy/pull/19497))
- Generate an export table only for separate compilation (Jukka Lehtosalo, PR [19521](https://github.com/python/mypy/pull/19521))
- Speed up `isinstance` with built‑in types (Piotr Sawicki, PR [19435](https://github.com/python/mypy/pull/19435))
- Use native integers for some sequence indexing (Jukka Lehtosalo, PR [19426](https://github.com/python/mypy/pull/19426))
- Speed up `isinstance(obj, list)` (Piotr Sawicki, PR [19416](https://github.com/python/mypy/pull/19416))
- Report error on reserved method names (Piotr Sawicki, PR [19407](https://github.com/python/mypy/pull/19407))
- Speed up string equality (Jukka Lehtosalo, PR [19402](https://github.com/python/mypy/pull/19402))
- Raise `NameError` on undefined names (Piotr Sawicki, PR [19395](https://github.com/python/mypy/pull/19395))
- Use per‑type freelists for nested functions (Jukka Lehtosalo, PR [19390](https://github.com/python/mypy/pull/19390))
- Simplify comparison of tuple elements (Piotr Sawicki, PR [19396](https://github.com/python/mypy/pull/19396))
- Generate introspection signatures for compiled functions (Brian Schubert, PR [19307](https://github.com/python/mypy/pull/19307))
- Fix undefined attribute checking special case (Jukka Lehtosalo, PR [19378](https://github.com/python/mypy/pull/19378))
- Fix comparison of tuples with different lengths (Piotr Sawicki, PR [19372](https://github.com/python/mypy/pull/19372))
- Speed up `list.clear` (Jahongir Qurbonov, PR [19344](https://github.com/python/mypy/pull/19344))
- Speed up `weakref.proxy` (BobTheBuidler, PR [19217](https://github.com/python/mypy/pull/19217))
- Speed up `weakref.ref` (BobTheBuidler, PR [19099](https://github.com/python/mypy/pull/19099))
- Speed up `str.count` (BobTheBuidler, PR [19264](https://github.com/python/mypy/pull/19264))

Stubtest Improvements
- Add temporary `--ignore-disjoint-bases` flag to ease PEP 800 migration (Joren Hammudoglu, PR [19740](https://github.com/python/mypy/pull/19740))
- Flag redundant uses of `disjoint_base` (Jelle Zijlstra, PR [19715](https://github.com/python/mypy/pull/19715))
- Improve signatures for `__init__` of C extension classes (Stephen Morton, PR [18259](https://github.com/python/mypy/pull/18259))
- Handle overloads with mixed positional‑only parameters (Stephen Morton, PR [18287](https://github.com/python/mypy/pull/18287))
- Use “parameter” (not “argument”) in error messages (PrinceNaroliya, PR [19707](https://github.com/python/mypy/pull/19707))
- Don’t require `disjoint_base` when `__slots__` imply finality (Jelle Zijlstra, PR [19701](https://github.com/python/mypy/pull/19701))
- Allow runtime‑existing aliases of `type_check_only` types (Brian Schubert, PR [19568](https://github.com/python/mypy/pull/19568))
- More detailed checking of type objects in stubtest (Stephen Morton, PR [18251](https://github.com/python/mypy/pull/18251))
- Support running stubtest in non-UTF8 terminals (Stanislav Terliakov, PR [19085](https://github.com/python/mypy/pull/19085))

Documentation Updates

- Add idlemypyextension to IDE integrations (CoolCat467, PR [18615](https://github.com/python/mypy/pull/18615))
- Document that `object` is often preferable to `Any` in APIs (wyattscarpenter, PR [19103](https://github.com/python/mypy/pull/19103))
- Include a detailed listing of flags enabled by `--strict` (wyattscarpenter, PR [19062](https://github.com/python/mypy/pull/19062))
- Update “common issues” (reveal_type/reveal_locals; note on orjson) (wyattscarpenter, PR [19059](https://github.com/python/mypy/pull/19059), [19058](https://github.com/python/mypy/pull/19058))

Other Notable Fixes and Improvements

- Remove deprecated `--new-type-inference` flag (the new algorithm has long been default) (Ivan Levkivskyi, PR [19570](https://github.com/python/mypy/pull/19570))
- Use empty context as a fallback for return expressions when outer context misleads inference (Ivan Levkivskyi, PR [19767](https://github.com/python/mypy/pull/19767))
- Fix forward references in type parameters of over‑parameterized PEP 695 aliases (Brian Schubert, PR [19725](https://github.com/python/mypy/pull/19725))
- Don’t expand PEP 695 aliases when checking node fullnames (Brian Schubert, PR [19699](https://github.com/python/mypy/pull/19699))
- Don’t use outer context for 'or' expression inference when LHS is Any (Stanislav Terliakov, PR [19748](https://github.com/python/mypy/pull/19748))
- Recognize buffer protocol special methods (Brian Schubert, PR [19581](https://github.com/python/mypy/pull/19581))
- Support attribute access on enum members correctly (Stanislav Terliakov, PR [19422](https://github.com/python/mypy/pull/19422))
- Check `__slots__` assignments on self types (Stanislav Terliakov, PR [19332](https://github.com/python/mypy/pull/19332))
- Move self‑argument checks after decorator application (Stanislav Terliakov, PR [19490](https://github.com/python/mypy/pull/19490))
- Infer empty list for `__slots__` and module `__all__` (Stanislav Terliakov, PR [19348](https://github.com/python/mypy/pull/19348))
- Use normalized tuples for fallback calculation (Stanislav Terliakov, PR [19111](https://github.com/python/mypy/pull/19111))
- Preserve literals when joining similar types (Stanislav Terliakov, PR [19279](https://github.com/python/mypy/pull/19279))
- Allow adjacent conditionally‑defined overloads (Stanislav Terliakov, PR [19042](https://github.com/python/mypy/pull/19042))
- Check property decorators more strictly (Stanislav Terliakov, PR [19313](https://github.com/python/mypy/pull/19313))
- Support properties with generic setters (Ivan Levkivskyi, PR [19298](https://github.com/python/mypy/pull/19298))
- Generalize class/static method and property alias support (Ivan Levkivskyi, PR [19297](https://github.com/python/mypy/pull/19297))
- Re‑widen custom properties after narrowing (Ivan Levkivskyi, PR [19296](https://github.com/python/mypy/pull/19296))
- Avoid erasing type objects when checking runtime cover (Shantanu, PR [19320](https://github.com/python/mypy/pull/19320))
- Include tuple fallback in constraints built from tuple types (Stanislav Terliakov, PR [19100](https://github.com/python/mypy/pull/19100))
- Somewhat better isinstance support on old‑style unions (Shantanu, PR [19714](https://github.com/python/mypy/pull/19714))
- Improve promotions inside unions (Christoph Tyralla, PR [19245](https://github.com/python/mypy/pull/19245))
- Treat uninhabited types as having all attributes (Ivan Levkivskyi, PR [19300](https://github.com/python/mypy/pull/19300))
- Improve metaclass conflict checks (Robsdedude, PR [17682](https://github.com/python/mypy/pull/17682))
- Fixes to metaclass resolution algorithm (Robsdedude, PR [17713](https://github.com/python/mypy/pull/17713))
- PEP 702 deprecated: handle “combined” overloads (Christoph Tyralla, PR [19626](https://github.com/python/mypy/pull/19626))
- PEP 702 deprecated: include overloads in snapshot descriptions (Christoph Tyralla, PR [19613](https://github.com/python/mypy/pull/19613))
- Ignore overload implementation when checking `__OP__` / `__rOP__` compatibility (Stanislav Terliakov, PR [18502](https://github.com/python/mypy/pull/18502))
- Support `_value_` as a fallback for ellipsis Enum members (Stanislav Terliakov, PR [19352](https://github.com/python/mypy/pull/19352))
- Sort arguments in TypedDict overlap messages (Marc Mueller, PR [19666](https://github.com/python/mypy/pull/19666))
- Fix handling of implicit return in lambda (Stanislav Terliakov, PR [19642](https://github.com/python/mypy/pull/19642))
- Improve behavior of uninhabited types (Stanislav Terliakov, PR [19648](https://github.com/python/mypy/pull/19648))
- Fix overload diagnostics when `*args` and `**kwargs` both match (Shantanu, PR [19614](https://github.com/python/mypy/pull/19614))
- Further fix overload diagnostics for `*args`/`**kwargs` (Shantanu, PR [19619](https://github.com/python/mypy/pull/19619))
- Show type variable name in "Cannot infer type argument" (Brian Schubert, PR [19290](https://github.com/python/mypy/pull/19290))
- Fail gracefully on unsupported template strings (PEP 750) (Brian Schubert, PR [19700](https://github.com/python/mypy/pull/19700))
- Revert colored argparse help for Python 3.14 (Marc Mueller, PR [19721](https://github.com/python/mypy/pull/19721))
- Update stubinfo for latest typeshed (Shantanu, PR [19771](https://github.com/python/mypy/pull/19771))
- Fix dict assignment when an incompatible same‑shape TypedDict exists (Stanislav Terliakov, PR [19592](https://github.com/python/mypy/pull/19592))
- Fix constructor type for subclasses of Any (Ivan Levkivskyi, PR [19295](https://github.com/python/mypy/pull/19295))
- Fix TypeGuard/TypeIs being forgotten in some cases (Brian Schubert, PR [19325](https://github.com/python/mypy/pull/19325))
- Fix TypeIs negative narrowing for unions of generics (Brian Schubert, PR [18193](https://github.com/python/mypy/pull/18193))
- dmypy suggest: Fix incorrect signature suggestion when a type matches a module name (Brian Schubert, PR [18937](https://github.com/python/mypy/pull/18937))
- dmypy suggest: Fix interaction with `__new__` (Stanislav Terliakov, PR [18966](https://github.com/python/mypy/pull/18966))
- dmypy suggest: Support Callable / callable Protocols in decorator unwrapping (Anthony Sottile, PR [19072](https://github.com/python/mypy/pull/19072))
- Fix missing error when redeclaring a type variable in a nested generic class (Brian Schubert, PR [18883](https://github.com/python/mypy/pull/18883))
- Fix for overloaded type object erasure (Shantanu, PR [19338](https://github.com/python/mypy/pull/19338))
- Fix TypeGuard with call on temporary object (Saul Shanabrook, PR [19577](https://github.com/python/mypy/pull/19577))

Typeshed Updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=2480d7e7c74493a024eaf254c5d2c6f452c80ee2+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:

- Ali Hamdan
- Anthony Sottile
- BobTheBuidler
- Brian Schubert
- Chainfire
- Charlie Denton
- Christoph Tyralla
- CoolCat467
- Daniel Hnyk
- Emily
- Emma Smith
- Ethan Sarp
- Ivan Levkivskyi
- Jahongir Qurbonov
- Jelle Zijlstra
- Joren Hammudoglu
- Jukka Lehtosalo
- Marc Mueller
- Omer Hadari
- Piotr Sawicki
- PrinceNaroliya
- Randolf Scholz
- Robsdedude
- Saul Shanabrook
- Shantanu
- Stanislav Terliakov
- Stephen Morton
- wyattscarpenter

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

1.15

We’ve just uploaded mypy 1.15 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).

Performance Improvements

Mypy is up to 40% faster in some use cases. This improvement comes largely from tuning the performance
of the garbage collector. Additionally, the release includes several micro-optimizations that may
be impactful for large projects.

Contributed by Jukka Lehtosalo
- PR [18306](https://github.com/python/mypy/pull/18306)
- PR [18302](https://github.com/python/mypy/pull/18302)
- PR [18298](https://github.com/python/mypy/pull/18298)
- PR [18299](https://github.com/python/mypy/pull/18299)

Mypyc Accelerated Mypy Wheels for ARM Linux

For best performance, mypy can be compiled to C extension modules using mypyc. This makes
mypy 3-5x faster than when interpreted with pure Python. We now build and upload mypyc
accelerated mypy wheels for `manylinux_aarch64` to PyPI, making it easy for Linux users on
ARM platforms to realise this speedup -- just `pip install` the latest mypy.

Contributed by Christian Bundy and Marc Mueller
(PR [mypy_mypyc-wheels76](https://github.com/mypyc/mypy_mypyc-wheels/pull/76),
PR [mypy_mypyc-wheels89](https://github.com/mypyc/mypy_mypyc-wheels/pull/89)).

`--strict-bytes`

By default, mypy treats `bytearray` and `memoryview` values as assignable to the `bytes`
type, for historical reasons. Use the `--strict-bytes` flag to disable this
behavior. [PEP 688](https://peps.python.org/pep-0688) specified the removal of this
special case. The flag will be enabled by default in **mypy 2.0**.

Contributed by Ali Hamdan (PR [18263](https://github.com/python/mypy/pull/18263)) and
Shantanu Jain (PR [13952](https://github.com/python/mypy/pull/13952)).

Improvements to Reachability Analysis and Partial Type Handling in Loops

This change results in mypy better modelling control flow within loops and hence detecting
several previously ignored issues. In some cases, this change may require additional
explicit variable annotations.

Contributed by Christoph Tyralla (PR [18180](https://github.com/python/mypy/pull/18180),
PR [18433](https://github.com/python/mypy/pull/18433)).

(Speaking of partial types, remember that we plan to enable `--local-partial-types`
by default in **mypy 2.0**.)

Better Discovery of Configuration Files

Mypy will now walk up the filesystem (up until a repository or file system root) to discover
configuration files. See the
[mypy configuration file documentation](https://mypy.readthedocs.io/en/stable/config_file.html)
for more details.

Contributed by Mikhail Shiryaev and Shantanu Jain
(PR [16965](https://github.com/python/mypy/pull/16965), PR [18482](https://github.com/python/mypy/pull/18482))

Better Line Numbers for Decorators and Slice Expressions

Mypy now uses more correct line numbers for decorators and slice expressions. In some cases,
you may have to change the location of a ` type: ignore` comment.

Contributed by Shantanu Jain (PR [18392](https://github.com/python/mypy/pull/18392),
PR [18397](https://github.com/python/mypy/pull/18397)).

Drop Support for Python 3.8

Mypy no longer supports running with Python 3.8, which has reached end-of-life.
When running mypy with Python 3.9+, it is still possible to type check code
that needs to support Python 3.8 with the `--python-version 3.8` argument.
Support for this will be dropped in the first half of 2025!

Contributed by Marc Mueller (PR [17492](https://github.com/python/mypy/pull/17492)).

Mypyc Improvements

* Fix `__init__` for classes with `attr.s(slots=True)` (Advait Dixit, PR [18447](https://github.com/python/mypy/pull/18447))
* Report error for nested class instead of crashing (Valentin Stanciu, PR [18460](https://github.com/python/mypy/pull/18460))
* Fix `InitVar` for dataclasses (Adv

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