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[Chore] Update changelog for 2.2 (#21691)
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‎CHANGELOG.md‎

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## Next Release
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## Mypy 2.2
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We've just uploaded mypy 2.2.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
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Mypy is a static type checker for Python. This release includes new features, performance
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improvements and bug fixes. You can install it as follows:
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python3 -m pip install -U mypy
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You can read the full documentation for this release on [Read the Docs](http://mypy.readthedocs.io).
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### Support for Closed TypedDicts (PEP 728)
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Mypy now supports closed TypedDicts as specified in PEP 728. A closed TypedDict cannot have extra
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keys beyond those explicitly defined. This allows the type checker to determine that certain
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operations are safe when they otherwise wouldn't be due to the potential presence of unknown keys.
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You can use the `closed` keyword argument with `TypedDict`:
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```python
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HasName = TypedDict("HasName", {"name": str})
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HasOnlyName = TypedDict("HasOnlyName", {"name": str}, closed=True)
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Movie = TypedDict("Movie", {"name": str, "year": int})
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movie: Movie = {"name": "Nimona", "year": 2023}
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has_name: HasName = movie # OK: HasName is open (default)
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has_only_name: HasOnlyName = movie # Error: HasOnlyName is closed and Movie has extra "year" key
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```
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Closed TypedDicts enable more precise type checking because the type checker knows exactly which
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keys are present. This is particularly useful when working with TypedDict unions or when you want
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to ensure that a TypedDict conforms to an exact shape.
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The `closed` keyword also enables safe type narrowing with `in` checks:
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```python
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Book = TypedDict('Book', {'book': str}, closed=True)
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DVD = TypedDict('DVD', {'dvd': str}, closed=True)
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type Inventory = Book | DVD
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def print_type(inventory: Inventory) -> None:
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if "book" in inventory:
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# Type is narrowed to Book here - safe because DVD is closed
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print(inventory["book"])
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else:
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# Type is narrowed to DVD here
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print(inventory["dvd"])
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```
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The `closed` keyword is also supported in class-based syntax:
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```python
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class HasOnlyName(TypedDict, closed=True):
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name: str
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```
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Note that closed TypedDicts are structural types, so a closed TypedDict is assignable to an open
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TypedDict with the same keys, but not vice versa.
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Contributed by Alice (PR [21382](https://github.com/python/mypy/pull/21382)).
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### Complete Support for Type Variable Defaults (PEP 696)
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Mypy now has complete support for type variable defaults as specified in PEP 696. This allows you to
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specify default values for type parameters in generic classes, functions, and type aliases.
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Traditional syntax (Python 3.11 and earlier):
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```python
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T = TypeVar("T", default=int) # This means that if no type is specified T = int
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@dataclass
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class Box(Generic[T]):
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value: T | None = None
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reveal_type(Box()) # type is Box[int]
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reveal_type(Box(value="Hello World!")) # type is Box[str]
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```
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New syntax (Python 3.12+):
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```python
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class Box[T = int]:
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def __init__(self, value: T) -> None:
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self.value = value
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reveal_type(Box()) # type is Box[int]
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reveal_type(Box(value="Hello World!")) # type is Box[str]
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```
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Type variable defaults work with all forms of generics, including classes, functions, and type aliases.
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This release completes the implementation by fixing various edge cases involving recursive defaults,
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dependencies between type variables, and interactions with variadic generics.
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Contributed by Ivan Levkivskyi (PRs [21491](https://github.com/python/mypy/pull/21491),
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[21526](https://github.com/python/mypy/pull/21526), [21544](https://github.com/python/mypy/pull/21544)).
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### Respect Explicit Return Type of `__new__()`
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Mypy now respects explicitly annotated return types in `__new__()` methods. Previously, mypy would
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always assume that `__new__()` returns an instance of the current class, ignoring explicit annotations.
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With this change, if you explicitly annotate a return type that differs from the implicit type, mypy
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will use the explicit annotation:
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```python
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class Factory:
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def __new__(cls) -> Product:
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return Product()
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reveal_type(Factory()) # type is Product, not Factory
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```
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Note that mypy still gives an error at the definition site if the explicit annotation is not a
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subtype of the current class, since this is technically not type-safe.
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For backwards compatibility, there are two exceptions:
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- If the return type is `Any`, mypy will still use the current class as the return type.
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- If the explicit return type comes from a superclass and is a supertype of the implicit return type,
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mypy will use the implicit (more specific) type:
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```python
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class A:
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def __new__(cls) -> A: ...
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reveal_type(A()) # type is A
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class B:
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def __new__(cls) -> B:
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return cls()
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class C(B): ...
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reveal_type(C()) # type is C
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```
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This fixes several long-standing issues where explicit `__new__()` return types were ignored.
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Contributed by Ivan Levkivskyi (PR [21441](https://github.com/python/mypy/pull/21441)).
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### TypeForm Support No Longer Experimental
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Support for `TypeForm` is no longer experimental. `TypeForm` (introduced in Python 3.14) allows you
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to annotate parameters that accept type expressions, providing better type checking for functions
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that work with types as values.
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```python
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from typing import TypeForm
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def make_list(tp: TypeForm[T]) -> list[T]:
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...
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# Correctly typed as list[int]
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int_list = make_list(int)
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```
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`TypeForm` support was previously reverted from mypy 2.1 due to a performance regression, but this
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has now been mitigated.
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Contributed by Ivan Levkivskyi and Jelle Zijlstra (PRs [21262](https://github.com/python/mypy/pull/21262), [21591](https://github.com/python/mypy/pull/21591),
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[21459](https://github.com/python/mypy/pull/21459)).
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### Experimental WASM Wheel for Python 3.14
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Mypy now ships an experimental WebAssembly (WASM) wheel for Python 3.14. This allows mypy to run
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in WASM environments such as Pyodide and browser-based Python implementations.
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The WASM wheel is considered experimental and may have limitations compared to native builds. Please
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report any issues you encounter when using mypy in WASM environments.
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Contributed by Ivan Levkivskyi (PR [21671](https://github.com/python/mypy/pull/21671)).
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### Mypyc Free-threading Improvements
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- Make function wrappers thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21620](https://github.com/python/mypy/pull/21620))
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- Make list remove and index thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21614](https://github.com/python/mypy/pull/21614))
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- Fix dict iteration memory safety on free-threaded builds (Jukka Lehtosalo, PR [21617](https://github.com/python/mypy/pull/21617))
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- Make some dict primitives thread-safe on free-threading builds (Jukka Lehtosalo, PR [21616](https://github.com/python/mypy/pull/21616))
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- Fix free-threading race condition in argument parsing (Jukka Lehtosalo, PR [21613](https://github.com/python/mypy/pull/21613))
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- Document free threading and other doc updates (Jukka Lehtosalo, PR [21494](https://github.com/python/mypy/pull/21494))
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### `librt.strings` Updates
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- Add `librt.strings.toupper` and `librt.strings.tolower` codepoint primitives (Vaggelis Danias, PR [21553](https://github.com/python/mypy/pull/21553))
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- Add `librt.strings.isidentifier` codepoint primitive (Vaggelis Danias, PR [21522](https://github.com/python/mypy/pull/21522))
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- Add `librt.strings.isalpha` codepoint primitive (Vaggelis Danias, PR [21521](https://github.com/python/mypy/pull/21521))
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- Add `librt.strings.isalnum` codepoint primitive (Vaggelis Danias, PR [21509](https://github.com/python/mypy/pull/21509))
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- Add `librt.strings.isdigit` codepoint primitive (Vaggelis Danias, PR [21504](https://github.com/python/mypy/pull/21504))
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- Add `librt.strings.isspace` char primitive (Vaggelis Danias, PR [21462](https://github.com/python/mypy/pull/21462))
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### Mypyc Improvements
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- Fix name lookup when class var and module var have the same name (Jukka Lehtosalo, PR [21594](https://github.com/python/mypy/pull/21594))
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- Report file and line number on uncaught exceptions (Jukka Lehtosalo, PR [21584](https://github.com/python/mypy/pull/21584))
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- Use `other` arg instead of `self` for RHS type (Ryan Heard, PR [21569](https://github.com/python/mypy/pull/21569))
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- Use `method_sig` to get the method signature (Ryan Heard, PR [21567](https://github.com/python/mypy/pull/21567))
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- Preserve inherited attribute defaults under `separate=True` (Jo, PR [21547](https://github.com/python/mypy/pull/21547))
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- Fix missing cross-group header deps in incremental builds (Jo, PR [21490](https://github.com/python/mypy/pull/21490))
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- Fix cross-group call to inherited `__mypyc_defaults_setup` (Jo, PR [21481](https://github.com/python/mypy/pull/21481))
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- Fix non-deterministic class struct layout under `separate=True` (Vaggelis Danias, PR [21530](https://github.com/python/mypy/pull/21530))
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- Specialize `s[i] == 'x'` to a codepoint int compare (Vaggelis Danias, PR [21579](https://github.com/python/mypy/pull/21579))
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- Fix reference leak in mypyc bytes concatenation (Colinxu2020, PR [21469](https://github.com/python/mypy/pull/21469))
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### Fixes to Crashes
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- Fix crash on invalid recursive variadic alias (Ivan Levkivskyi, PR [21572](https://github.com/python/mypy/pull/21572))
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- Fix crashes on variadic unpacking in synthetic types (Ivan Levkivskyi, PR [21555](https://github.com/python/mypy/pull/21555))
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- Fix crash on unhandled meet variadic tuple vs instance (Ivan Levkivskyi, PR [21558](https://github.com/python/mypy/pull/21558))
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- Fix crash on deferred generic class nested in function (Ivan Levkivskyi, PR [21557](https://github.com/python/mypy/pull/21557))
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- Fix crash in new-style type alias with variadic unpack (Ivan Levkivskyi, PR [21551](https://github.com/python/mypy/pull/21551))
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- Fix various crashes on recursive type variable defaults (Ivan Levkivskyi, PR [21491](https://github.com/python/mypy/pull/21491))
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- Fix crash for empty `Annotated` type application (Rayan Salhab, PR [21503](https://github.com/python/mypy/pull/21503))
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- Fix crash on `Unpack` used without arguments in class bases (Sai Asish Y, PR [21470](https://github.com/python/mypy/pull/21470))
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### Performance Improvements
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- Memoize the options snapshot (Kevin Kannammalil, PR [21354](https://github.com/python/mypy/pull/21354))
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- Don't include `not_ready_deps` tracking as relating to mypy internals (Kevin Kannammalil, PR [21389](https://github.com/python/mypy/pull/21389))
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- Speed up transitive dependency hash for singleton SCCs (Kevin Kannammalil, PR [21390](https://github.com/python/mypy/pull/21390))
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- Optimize typeform checks (Jelle Zijlstra, PR [21459](https://github.com/python/mypy/pull/21459))
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### Improvements to the Native Parser
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- Support `--shadow-file` with `--native-parser` (Jukka Lehtosalo, PR [21623](https://github.com/python/mypy/pull/21623))
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- Add Python version checks to native parser (Kevin Kannammalil, PR [21539](https://github.com/python/mypy/pull/21539))
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- Allow nativeparse to parse source code directly (bzoracler, PR [21260](https://github.com/python/mypy/pull/21260))
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### Other Notable Fixes and Improvements
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- Add function definition notes for `too many positional arguments` errors (Kevin Kannammalil, PR [21410](https://github.com/python/mypy/pull/21410))
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- Fix the exportjson tool (.ff cache to .json conversion) (Jukka Lehtosalo, PR [21628](https://github.com/python/mypy/pull/21628))
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- Support floats in JSON in fixed-format cache (Ivan Levkivskyi, PR [21603](https://github.com/python/mypy/pull/21603))
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- Update `TypedDictType.__init__` signature to preserve backward compat (Jukka Lehtosalo, PR [21590](https://github.com/python/mypy/pull/21590))
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- Fix constructor calls for union-bounded `TypeVar`s (Jingchen Ye, PR [21571](https://github.com/python/mypy/pull/21571))
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- Fix `TypedDict` indexing with literal keys in comprehensions (Jingchen Ye, PR [21556](https://github.com/python/mypy/pull/21556))
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- Correctly handle empty tuple index when unpacked (Ivan Levkivskyi, PR [21545](https://github.com/python/mypy/pull/21545))
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- Support protocol checks for self-types in tuple types (Ivan Levkivskyi, PR [21535](https://github.com/python/mypy/pull/21535))
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- Fix edge cases in variadic tuple subclasses (Ivan Levkivskyi, PR [21518](https://github.com/python/mypy/pull/21518))
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- Special-case constructor for tuple types (Ivan Levkivskyi, PR [21502](https://github.com/python/mypy/pull/21502))
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- Fix false positive "Expected TypedDict key to be string literal" for `Union[TypedDict, dict[K, V]]` (Zakir Jiwani, PR [21511](https://github.com/python/mypy/pull/21511))
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- Use explicit `Never` for type inference (Ivan Levkivskyi, PR [21497](https://github.com/python/mypy/pull/21497))
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- Narrow membership in statically known containers (Shantanu, PR [21461](https://github.com/python/mypy/pull/21461))
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- Improve negative narrowing for membership checks on tuples (Shantanu, PR [21456](https://github.com/python/mypy/pull/21456))
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- Analyze `TypedDict` decorators (Pranav Manglik, PR [21267](https://github.com/python/mypy/pull/21267))
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- Start testing Python 3.15 (Marc Mueller, PR [21439](https://github.com/python/mypy/pull/21439))
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- Improved handling of `NamedTuple`, `TypedDict`, `Enum`, and regular classes nested in functions (Ivan Levkivskyi, PR [21478](https://github.com/python/mypy/pull/21478))
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### Typeshed Updates
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Please see [git log](https://github.com/python/typeshed/commits/main?after=616424285beccaa76f90e87e1e922b1dc68710ca+0&branch=main&path=stdlib) for full list of standard library typeshed stub changes.
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### Acknowledgements
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Thanks to all mypy contributors who contributed to this release:
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- Adam Turner
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- alicederyn
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- bzoracler
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- Colinxu2020
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- georgesittas
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- Ivan Levkivskyi
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- Jelle Zijlstra
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- Jingchen Ye
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- Jukka Lehtosalo
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- Kevin Kannammalil
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- lphuc2250gma
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- Marc Mueller
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- Pranav Manglik
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- Rayan Salhab
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- Ryan Heard
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- Sai Asish Y
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- Shantanu
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- sobolevn
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- Vaggelis Danias
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- Victor Letichevsky
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- Zakir Jiwani
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I'd also like to thank my employer, Dropbox, for supporting mypy development.
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## Mypy 2.1
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We’ve just uploaded mypy 2.1.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).

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