Update mypy to 1.19.0

[pyup-bot]

This PR updates mypy from 1.18.2 to 1.19.0.

Changelog

1.19

We’ve just uploaded mypy 1.19.0 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).

Python 3.9 Support Ending Soon

This is the last mypy feature release that supports Python 3.9, which reached
end of life in October 2025.

Performance Improvements
- Switch to a more dynamic SCC processing logic (Ivan Levkivskyi, PR [20053](https://github.com/python/mypy/pull/20053))
- Speed up type aliases (Ivan Levkivskyi, PR [19810](https://github.com/python/mypy/pull/19810))

Fixed‑Format Cache Improvements

Mypy uses a cache by default to speed up incremental runs by reusing partial results
from earlier runs. Mypy 1.18 added a new binary fixed-format cache representation as
an experimental feature. The feature is no longer experimental, and we are planning
to enable it by default in a future mypy release (possibly 1.20), since it's faster
and uses less space than the original, JSON-based cache format. Use
`--fixed-format-cache` to enable the fixed-format cache.

Mypy now has an extra dependency on the `librt` PyPI package, as it's needed for
cache serialization and deserialization.

Mypy ships with a tool to convert fixed-format cache files to the old JSON format.
Example of how to use this:

$ python -m mypy.exportjson .mypy_cache/.../my_module.data.ff


This way existing use cases that parse JSON cache files can be supported when using
the new format, though an extra conversion step is needed.

This release includes these improvements:

- Force-discard cache if cache format changed (Ivan Levkivskyi, PR [20152](https://github.com/python/mypy/pull/20152))
- Add tool to convert binary cache files to JSON (Jukka Lehtosalo, PR [20071](https://github.com/python/mypy/pull/20071))
- Use more efficient serialization format for long integers in cache files (Jukka Lehtosalo, PR [20151](https://github.com/python/mypy/pull/20151))
- More robust packing of floats in fixed-format cache (Ivan Levkivskyi, PR [20150](https://github.com/python/mypy/pull/20150))
- Use self-descriptive cache with type tags (Ivan Levkivskyi, PR [20137](https://github.com/python/mypy/pull/20137))
- Use fixed format for cache metas (Ivan Levkivskyi, PR [20088](https://github.com/python/mypy/pull/20088))
- Make metas more compact; fix indirect suppression (Ivan Levkivskyi, PR [20075](https://github.com/python/mypy/pull/20075))
- Use dedicated tags for most common cached instances (Ivan Levkivskyi, PR [19762](https://github.com/python/mypy/pull/19762))

PEP 747: Annotating Type Forms

Mypy now recognizes `TypeForm[T]` as a type and implements
[PEP 747](https://peps.python.org/pep-0747/). The feature is still experimental,
and it's disabled by default. Use `--enable-incomplete-feature=TypeForm` to
enable type forms. A type form object captures the type information provided by a
runtime type expression. Example:

python
from typing_extensions import TypeForm

def trycast[T](typx: TypeForm[T], value: object) -> T | None: ...

def example(o: object) -> None:
  'int | str' below is an expression that represents a type.
  Unlike type[T], TypeForm[T] can be used with all kinds of types,
  including union types.
 x = trycast(int | str, o)
 if x is not None:
      Type of 'x' is 'int | str' here
     ...


This feature was contributed by David Foster (PR [19596](https://github.com/python/mypy/pull/19596)).

Fixes to Crashes
- Do not push partial types to the binder (Stanislav Terliakov, PR [20202](https://github.com/python/mypy/pull/20202))
- Fix crash on recursive tuple with Hashable (Ivan Levkivskyi, PR [20232](https://github.com/python/mypy/pull/20232))
- Fix crash related to decorated functions (Stanislav Terliakov, PR [20203](https://github.com/python/mypy/pull/20203))
- Do not abort constructing TypeAlias if only type parameters hold us back (Stanislav Terliakov, PR [20162](https://github.com/python/mypy/pull/20162))
- Use the fallback for `ModuleSpec` early if it can never be resolved (Stanislav Terliakov, PR [20167](https://github.com/python/mypy/pull/20167))
- Do not store deferred NamedTuple fields as redefinitions (Stanislav Terliakov, PR [20147](https://github.com/python/mypy/pull/20147))
- Discard partial types remaining after inference failure (Stanislav Terliakov, PR [20126](https://github.com/python/mypy/pull/20126))
- Fix an infinite recursion bug (Stanislav Terliakov, PR [20127](https://github.com/python/mypy/pull/20127))
- Fix IsADirectoryError for namespace packages when using --linecoverage-report (wyattscarpenter, PR [20109](https://github.com/python/mypy/pull/20109))
- Fix an internal error when creating cobertura output for namespace package (wyattscarpenter, PR [20112](https://github.com/python/mypy/pull/20112))
- Allow type parameters reusing the name missing from current module (Stanislav Terliakov, PR [20081](https://github.com/python/mypy/pull/20081))
- Prevent TypeGuardedType leak from narrowing declared type as part of type variable bound (Stanislav Terliakov, PR [20046](https://github.com/python/mypy/pull/20046))
- Fix crash on invalid unpack in base class (Ivan Levkivskyi, PR [19962](https://github.com/python/mypy/pull/19962))
- Traverse ParamSpec prefix where we should (Ivan Levkivskyi, PR [19800](https://github.com/python/mypy/pull/19800))
- Fix daemon crash related to imports (Ivan Levkivskyi, PR [20271](https://github.com/python/mypy/pull/20271))

Mypyc: Support for `__getattr__`, `__setattr__`, and `__delattr__`

Mypyc now has partial support for `__getattr__`, `__setattr__` and
`__delattr__` methods in native classes.

Note that native attributes are not stored using `__dict__`. Setting attributes
directly while bypassing `__setattr__` is possible by using
`super().__setattr__(...)` or `object.__setattr__(...)`, but not via `__dict__`.

Example:
python
class Demo:
 _data: dict[str, str]

 def __init__(self) -> None:
      Initialize data dict without calling our __setattr__
     super().__setattr__("_data", {})

 def __setattr__(self, name: str, value: str) -> None:
     print(f"Setting {name} = {value!r}")

     if name == "_data":
         raise AttributeError("'_data' cannot be set")

     self._data[name] = value

 def __getattr__(self, name: str) -> str:
     print(f"Getting {name}")

     try:
         return self._data[name]
     except KeyError:
         raise AttributeError(name)

d = Demo()
d.x = "hello"
d.y = "world"

print(d.x)
print(d.y)


Related PRs:
- Generate `__setattr__` wrapper (Piotr Sawicki, PR [19937](https://github.com/python/mypy/pull/19937))
- Generate `__getattr__` wrapper (Piotr Sawicki, PR [19909](https://github.com/python/mypy/pull/19909))
- Support deleting attributes in `__setattr__` wrapper (Piotr Sawicki, PR [19997](https://github.com/python/mypy/pull/19997))

Miscellaneous Mypyc Improvements
- Fix `__new__` in native classes with inheritance (Piotr Sawicki, PR [20302](https://github.com/python/mypy/pull/20302))
- Fix crash on `super` in generator (Ivan Levkivskyi, PR [20291](https://github.com/python/mypy/pull/20291))
- Fix calling base class async method using `super()` (Jukka Lehtosalo, PR [20254](https://github.com/python/mypy/pull/20254))
- Fix async or generator methods in traits (Jukka Lehtosalo, PR [20246](https://github.com/python/mypy/pull/20246))
- Optimize equality check with string literals (BobTheBuidler, PR [19883](https://github.com/python/mypy/pull/19883))
- Fix inheritance of async defs (Jukka Lehtosalo, PR [20044](https://github.com/python/mypy/pull/20044))
- Reject invalid `mypyc_attr` args (BobTheBuidler, PR [19963](https://github.com/python/mypy/pull/19963))
- Optimize `isinstance` with tuple of primitive types (BobTheBuidler, PR [19949](https://github.com/python/mypy/pull/19949))
- Optimize away first index check in for loops if length > 1 (BobTheBuidler, PR [19933](https://github.com/python/mypy/pull/19933))
- Fix broken exception/cancellation handling in async def (Jukka Lehtosalo, PR [19951](https://github.com/python/mypy/pull/19951))
- Transform `object.__new__` inside `__new__` (Piotr Sawicki, PR [19866](https://github.com/python/mypy/pull/19866))
- Fix crash with NewType and other non-class types in incremental builds (Jukka Lehtosalo, PR [19837](https://github.com/python/mypy/pull/19837))
- Optimize container creation from expressions with length known at compile time (BobTheBuidler, PR [19503](https://github.com/python/mypy/pull/19503))
- Allow per-class free list to be used with inheritance (Jukka Lehtosalo, PR [19790](https://github.com/python/mypy/pull/19790))
- Fix object finalization (Marc Mueller, PR [19749](https://github.com/python/mypy/pull/19749))
- Allow defining a single-item free "list" for a native class (Jukka Lehtosalo, PR [19785](https://github.com/python/mypy/pull/19785))
- Speed up unary "not" (Jukka Lehtosalo, PR [19774](https://github.com/python/mypy/pull/19774))

Stubtest Improvements
- Check `_value_` for ellipsis-valued stub enum members (Stanislav Terliakov, PR [19760](https://github.com/python/mypy/pull/19760))
- Include function name in overload assertion messages (Joren Hammudoglu, PR [20063](https://github.com/python/mypy/pull/20063))
- Fix special case in analyzing function signature (iap, PR [19822](https://github.com/python/mypy/pull/19822))
- Improve `allowlist` docs with better example (sobolevn, PR [20007](https://github.com/python/mypy/pull/20007))

Documentation Updates
- Update duck type compatibility: mention strict-bytes and mypy 2.0 (wyattscarpenter, PR [20121](https://github.com/python/mypy/pull/20121))
- Document `--enable-incomplete-feature TypeForm` (wyattscarpenter, PR [20173](https://github.com/python/mypy/pull/20173))
- Change the inline TypedDict example (wyattscarpenter, PR [20172](https://github.com/python/mypy/pull/20172))
- Replace `List` with built‑in `list` (PEP 585) (Thiago J. Barbalho, PR [20000](https://github.com/python/mypy/pull/20000))
- Improve junit documentation (wyattscarpenter, PR [19867](https://github.com/python/mypy/pull/19867))

Other Notable Fixes and Improvements
- Fix annotated with function as type keyword list parameter (KarelKenens, PR [20094](https://github.com/python/mypy/pull/20094))
- Fix errors for raise NotImplemented (Shantanu, PR [20168](https://github.com/python/mypy/pull/20168))
- Don't let help formatter line-wrap URLs (Frank Dana, PR [19825](https://github.com/python/mypy/pull/19825))
- Do not cache fast container types inside lambdas (Stanislav Terliakov, PR [20166](https://github.com/python/mypy/pull/20166))
- Respect force-union-syntax flag in error hint (Marc Mueller, PR [20165](https://github.com/python/mypy/pull/20165))
- Fix type checking of dict type aliases (Shantanu, PR [20170](https://github.com/python/mypy/pull/20170))
- Use pretty callable formatting more often for callable expressions (Theodore Ando, PR [20128](https://github.com/python/mypy/pull/20128))
- Use dummy concrete type instead of `Any` when checking protocol variance (bzoracler, PR [20110](https://github.com/python/mypy/pull/20110))
- PEP 696: Fix swapping TypeVars with defaults (Randolf Scholz, PR [19449](https://github.com/python/mypy/pull/19449))
- Fix narrowing of class pattern with union type (Randolf Scholz, PR [19517](https://github.com/python/mypy/pull/19517))
- Do not emit unreachable warnings for lines that return `NotImplemented` (Christoph Tyralla, PR [20083](https://github.com/python/mypy/pull/20083))
- Fix matching against `typing.Callable` and `Protocol` types (Randolf Scholz, PR [19471](https://github.com/python/mypy/pull/19471))
- Make `--pretty` work better on multi-line issues (A5rocks, PR [20056](https://github.com/python/mypy/pull/20056))
- More precise return types for `TypedDict.get` (Randolf Scholz, PR [19897](https://github.com/python/mypy/pull/19897))
- Prevent false unreachable warnings for `final` instances that occur when strict optional checking is disabled (Christoph Tyralla, PR [20045](https://github.com/python/mypy/pull/20045))
- Check class references to catch non-existent classes in match cases (A5rocks, PR [20042](https://github.com/python/mypy/pull/20042))
- Do not sort unused error codes in unused error codes warning (wyattscarpenter, PR [20036](https://github.com/python/mypy/pull/20036))
- Fix `[name-defined]` false positive in `class A[X, Y=X]:` case (sobolevn, PR [20021](https://github.com/python/mypy/pull/20021))
- Filter SyntaxWarnings during AST parsing (Marc Mueller, PR [20023](https://github.com/python/mypy/pull/20023))
- Make untyped decorator its own error code (wyattscarpenter, PR [19911](https://github.com/python/mypy/pull/19911))
- Support error codes from plugins in options (Sigve Sebastian Farstad, PR [19719](https://github.com/python/mypy/pull/19719))
- Allow returning Literals in `__new__` (James Hilton-Balfe, PR [15687](https://github.com/python/mypy/pull/15687))
- Inverse interface freshness logic (Ivan Levkivskyi, PR [19809](https://github.com/python/mypy/pull/19809))
- Do not report exhaustive-match after deferral (Stanislav Terliakov, PR [19804](https://github.com/python/mypy/pull/19804))
- Make `untyped_calls_exclude` invalidate cache (Ivan Levkivskyi, PR [19801](https://github.com/python/mypy/pull/19801))
- Add await to empty context hack (Stanislav Terliakov, PR [19777](https://github.com/python/mypy/pull/19777))
- Consider non-empty enums assignable to Self (Stanislav Terliakov, PR [19779](https://github.com/python/mypy/pull/19779))

Typeshed updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=ebce8d766b41fbf4d83cf47c1297563a9508ff60+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:
- A5rocks
- BobTheBuidler
- bzoracler
- Chainfire
- Christoph Tyralla
- David Foster
- Frank Dana
- Guo Ci
- iap
- Ivan Levkivskyi
- James Hilton-Balfe
- jhance
- Joren Hammudoglu
- Jukka Lehtosalo
- KarelKenens
- Kevin Kannammalil
- Marc Mueller
- Michael Carlstrom
- Michael J. Sullivan
- Piotr Sawicki
- Randolf Scholz
- Shantanu
- Sigve Sebastian Farstad
- sobolevn
- Stanislav Terliakov
- Stephen Morton
- Theodore Ando
- Thiago J. Barbalho
- wyattscarpenter

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

Links

• PyPI: https://pypi.org/project/mypy
• Changelog: https://data.safetycli.com/changelogs/mypy/