diff --git a/CHANGELOG.md b/CHANGELOG.md index 2a2c9191b71a..02739ef6591f 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -2,6 +2,283 @@ ## Next Release +## Mypy 2.2 + +We've just uploaded mypy 2.2.0 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 for Closed TypedDicts (PEP 728) + +Mypy now supports closed TypedDicts as specified in PEP 728. A closed TypedDict cannot have extra +keys beyond those explicitly defined. This allows the type checker to determine that certain +operations are safe when they otherwise wouldn't be due to the potential presence of unknown keys. + +You can use the `closed` keyword argument with `TypedDict`: + +```python +HasName = TypedDict("HasName", {"name": str}) +HasOnlyName = TypedDict("HasOnlyName", {"name": str}, closed=True) +Movie = TypedDict("Movie", {"name": str, "year": int}) + +movie: Movie = {"name": "Nimona", "year": 2023} +has_name: HasName = movie # OK: HasName is open (default) +has_only_name: HasOnlyName = movie # Error: HasOnlyName is closed and Movie has extra "year" key +``` + +Closed TypedDicts enable more precise type checking because the type checker knows exactly which +keys are present. This is particularly useful when working with TypedDict unions or when you want +to ensure that a TypedDict conforms to an exact shape. + +The `closed` keyword also enables safe type narrowing with `in` checks: + +```python +Book = TypedDict('Book', {'book': str}, closed=True) +DVD = TypedDict('DVD', {'dvd': str}, closed=True) +type Inventory = Book | DVD + +def print_type(inventory: Inventory) -> None: + if "book" in inventory: + # Type is narrowed to Book here - safe because DVD is closed + print(inventory["book"]) + else: + # Type is narrowed to DVD here + print(inventory["dvd"]) +``` + +The `closed` keyword is also supported in class-based syntax: + +```python +class HasOnlyName(TypedDict, closed=True): + name: str +``` + +Note that closed TypedDicts are structural types, so a closed TypedDict is assignable to an open +TypedDict with the same keys, but not vice versa. + +Contributed by Alice (PR [21382](https://github.com/python/mypy/pull/21382)). + +### Complete Support for Type Variable Defaults (PEP 696) + +Mypy now has complete support for type variable defaults as specified in PEP 696. This allows you to +specify default values for type parameters in generic classes, functions, and type aliases. + +Traditional syntax (Python 3.11 and earlier): + +```python +T = TypeVar("T", default=int) # This means that if no type is specified T = int + +@dataclass +class Box(Generic[T]): + value: T | None = None + +reveal_type(Box()) # type is Box[int] +reveal_type(Box(value="Hello World!")) # type is Box[str] +``` + +New syntax (Python 3.12+): + +```python +class Box[T = int]: + def __init__(self, value: T) -> None: + self.value = value + +reveal_type(Box()) # type is Box[int] +reveal_type(Box(value="Hello World!")) # type is Box[str] +``` + +Type variable defaults work with all forms of generics, including classes, functions, and type aliases. +This release completes the implementation by fixing various edge cases involving recursive defaults, +dependencies between type variables, and interactions with variadic generics. + +Contributed by Ivan Levkivskyi (PRs [21491](https://github.com/python/mypy/pull/21491), +[21526](https://github.com/python/mypy/pull/21526), [21544](https://github.com/python/mypy/pull/21544)). + +### Respect Explicit Return Type of `__new__()` + +Mypy now respects explicitly annotated return types in `__new__()` methods. Previously, mypy would +always assume that `__new__()` returns an instance of the current class, ignoring explicit annotations. + +With this change, if you explicitly annotate a return type that differs from the implicit type, mypy +will use the explicit annotation: + +```python +class Factory: + def __new__(cls) -> Product: + return Product() + +reveal_type(Factory()) # type is Product, not Factory +``` + +Note that mypy still gives an error at the definition site if the explicit annotation is not a +subtype of the current class, since this is technically not type-safe. + +For backwards compatibility, there are two exceptions: +- If the return type is `Any`, mypy will still use the current class as the return type. +- If the explicit return type comes from a superclass and is a supertype of the implicit return type, + mypy will use the implicit (more specific) type: + +```python +class A: + def __new__(cls) -> A: ... + +reveal_type(A()) # type is A + +class B: + def __new__(cls) -> B: + return cls() + +class C(B): ... +reveal_type(C()) # type is C +``` + +This fixes several long-standing issues where explicit `__new__()` return types were ignored. + +Contributed by Ivan Levkivskyi (PR [21441](https://github.com/python/mypy/pull/21441)). + +### TypeForm Support No Longer Experimental + +Support for `TypeForm` is no longer experimental. `TypeForm` (introduced in Python 3.14) allows you +to annotate parameters that accept type expressions, providing better type checking for functions +that work with types as values. + +```python +from typing import TypeForm + +def make_list(tp: TypeForm[T]) -> list[T]: + ... + +# Correctly typed as list[int] +int_list = make_list(int) +``` + +`TypeForm` support was previously reverted from mypy 2.1 due to a performance regression, but this +has now been mitigated. + +Contributed by Ivan Levkivskyi and Jelle Zijlstra (PRs [21262](https://github.com/python/mypy/pull/21262), [21591](https://github.com/python/mypy/pull/21591), +[21459](https://github.com/python/mypy/pull/21459)). + +### Experimental WASM Wheel for Python 3.14 + +Mypy now ships an experimental WebAssembly (WASM) wheel for Python 3.14. This allows mypy to run +in WASM environments such as Pyodide and browser-based Python implementations. + +The WASM wheel is considered experimental and may have limitations compared to native builds. Please +report any issues you encounter when using mypy in WASM environments. + +Contributed by Ivan Levkivskyi (PR [21671](https://github.com/python/mypy/pull/21671)). + +### Mypyc Free-threading Improvements + +- Make function wrappers thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21620](https://github.com/python/mypy/pull/21620)) +- Make list remove and index thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21614](https://github.com/python/mypy/pull/21614)) +- Fix dict iteration memory safety on free-threaded builds (Jukka Lehtosalo, PR [21617](https://github.com/python/mypy/pull/21617)) +- Make some dict primitives thread-safe on free-threading builds (Jukka Lehtosalo, PR [21616](https://github.com/python/mypy/pull/21616)) +- Fix free-threading race condition in argument parsing (Jukka Lehtosalo, PR [21613](https://github.com/python/mypy/pull/21613)) +- Document free threading and other doc updates (Jukka Lehtosalo, PR [21494](https://github.com/python/mypy/pull/21494)) + +### `librt.strings` Updates + +- Add `librt.strings.toupper` and `librt.strings.tolower` codepoint primitives (Vaggelis Danias, PR [21553](https://github.com/python/mypy/pull/21553)) +- Add `librt.strings.isidentifier` codepoint primitive (Vaggelis Danias, PR [21522](https://github.com/python/mypy/pull/21522)) +- Add `librt.strings.isalpha` codepoint primitive (Vaggelis Danias, PR [21521](https://github.com/python/mypy/pull/21521)) +- Add `librt.strings.isalnum` codepoint primitive (Vaggelis Danias, PR [21509](https://github.com/python/mypy/pull/21509)) +- Add `librt.strings.isdigit` codepoint primitive (Vaggelis Danias, PR [21504](https://github.com/python/mypy/pull/21504)) +- Add `librt.strings.isspace` char primitive (Vaggelis Danias, PR [21462](https://github.com/python/mypy/pull/21462)) + +### Mypyc Improvements + +- Fix name lookup when class var and module var have the same name (Jukka Lehtosalo, PR [21594](https://github.com/python/mypy/pull/21594)) +- Report file and line number on uncaught exceptions (Jukka Lehtosalo, PR [21584](https://github.com/python/mypy/pull/21584)) +- Use `other` arg instead of `self` for RHS type (Ryan Heard, PR [21569](https://github.com/python/mypy/pull/21569)) +- Use `method_sig` to get the method signature (Ryan Heard, PR [21567](https://github.com/python/mypy/pull/21567)) +- Preserve inherited attribute defaults under `separate=True` (Jo, PR [21547](https://github.com/python/mypy/pull/21547)) +- Fix missing cross-group header deps in incremental builds (Jo, PR [21490](https://github.com/python/mypy/pull/21490)) +- Fix cross-group call to inherited `__mypyc_defaults_setup` (Jo, PR [21481](https://github.com/python/mypy/pull/21481)) +- Fix non-deterministic class struct layout under `separate=True` (Vaggelis Danias, PR [21530](https://github.com/python/mypy/pull/21530)) +- Specialize `s[i] == 'x'` to a codepoint int compare (Vaggelis Danias, PR [21579](https://github.com/python/mypy/pull/21579)) +- Fix reference leak in mypyc bytes concatenation (Colinxu2020, PR [21469](https://github.com/python/mypy/pull/21469)) + +### Fixes to Crashes + +- Fix crash on invalid recursive variadic alias (Ivan Levkivskyi, PR [21572](https://github.com/python/mypy/pull/21572)) +- Fix crashes on variadic unpacking in synthetic types (Ivan Levkivskyi, PR [21555](https://github.com/python/mypy/pull/21555)) +- Fix crash on unhandled meet variadic tuple vs instance (Ivan Levkivskyi, PR [21558](https://github.com/python/mypy/pull/21558)) +- Fix crash on deferred generic class nested in function (Ivan Levkivskyi, PR [21557](https://github.com/python/mypy/pull/21557)) +- Fix crash in new-style type alias with variadic unpack (Ivan Levkivskyi, PR [21551](https://github.com/python/mypy/pull/21551)) +- Fix various crashes on recursive type variable defaults (Ivan Levkivskyi, PR [21491](https://github.com/python/mypy/pull/21491)) +- Fix crash for empty `Annotated` type application (Rayan Salhab, PR [21503](https://github.com/python/mypy/pull/21503)) +- Fix crash on `Unpack` used without arguments in class bases (Sai Asish Y, PR [21470](https://github.com/python/mypy/pull/21470)) + +### Performance Improvements + +- Memoize the options snapshot (Kevin Kannammalil, PR [21354](https://github.com/python/mypy/pull/21354)) +- Don't include `not_ready_deps` tracking as relating to mypy internals (Kevin Kannammalil, PR [21389](https://github.com/python/mypy/pull/21389)) +- Speed up transitive dependency hash for singleton SCCs (Kevin Kannammalil, PR [21390](https://github.com/python/mypy/pull/21390)) +- Optimize typeform checks (Jelle Zijlstra, PR [21459](https://github.com/python/mypy/pull/21459)) + +### Improvements to the Native Parser + +- Support `--shadow-file` with `--native-parser` (Jukka Lehtosalo, PR [21623](https://github.com/python/mypy/pull/21623)) +- Add Python version checks to native parser (Kevin Kannammalil, PR [21539](https://github.com/python/mypy/pull/21539)) +- Allow nativeparse to parse source code directly (bzoracler, PR [21260](https://github.com/python/mypy/pull/21260)) + +### Other Notable Fixes and Improvements + +- Add function definition notes for `too many positional arguments` errors (Kevin Kannammalil, PR [21410](https://github.com/python/mypy/pull/21410)) +- Fix the exportjson tool (.ff cache to .json conversion) (Jukka Lehtosalo, PR [21628](https://github.com/python/mypy/pull/21628)) +- Support floats in JSON in fixed-format cache (Ivan Levkivskyi, PR [21603](https://github.com/python/mypy/pull/21603)) +- Update `TypedDictType.__init__` signature to preserve backward compat (Jukka Lehtosalo, PR [21590](https://github.com/python/mypy/pull/21590)) +- Fix constructor calls for union-bounded `TypeVar`s (Jingchen Ye, PR [21571](https://github.com/python/mypy/pull/21571)) +- Fix `TypedDict` indexing with literal keys in comprehensions (Jingchen Ye, PR [21556](https://github.com/python/mypy/pull/21556)) +- Correctly handle empty tuple index when unpacked (Ivan Levkivskyi, PR [21545](https://github.com/python/mypy/pull/21545)) +- Support protocol checks for self-types in tuple types (Ivan Levkivskyi, PR [21535](https://github.com/python/mypy/pull/21535)) +- Fix edge cases in variadic tuple subclasses (Ivan Levkivskyi, PR [21518](https://github.com/python/mypy/pull/21518)) +- Special-case constructor for tuple types (Ivan Levkivskyi, PR [21502](https://github.com/python/mypy/pull/21502)) +- 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)) +- Use explicit `Never` for type inference (Ivan Levkivskyi, PR [21497](https://github.com/python/mypy/pull/21497)) +- Narrow membership in statically known containers (Shantanu, PR [21461](https://github.com/python/mypy/pull/21461)) +- Improve negative narrowing for membership checks on tuples (Shantanu, PR [21456](https://github.com/python/mypy/pull/21456)) +- Analyze `TypedDict` decorators (Pranav Manglik, PR [21267](https://github.com/python/mypy/pull/21267)) +- Start testing Python 3.15 (Marc Mueller, PR [21439](https://github.com/python/mypy/pull/21439)) +- Improved handling of `NamedTuple`, `TypedDict`, `Enum`, and regular classes nested in functions (Ivan Levkivskyi, PR [21478](https://github.com/python/mypy/pull/21478)) + +### Typeshed Updates + +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. + +### Acknowledgements + +Thanks to all mypy contributors who contributed to this release: + +- Adam Turner +- alicederyn +- bzoracler +- Colinxu2020 +- georgesittas +- Ivan Levkivskyi +- Jelle Zijlstra +- Jingchen Ye +- Jukka Lehtosalo +- Kevin Kannammalil +- lphuc2250gma +- Marc Mueller +- Pranav Manglik +- Rayan Salhab +- Ryan Heard +- Sai Asish Y +- Shantanu +- sobolevn +- Vaggelis Danias +- Victor Letichevsky +- Zakir Jiwani + +I'd also like to thank my employer, Dropbox, for supporting mypy development. + ## Mypy 2.1 We’ve just uploaded mypy 2.1.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).