Update mypy to 1.19.0

[pyup-bot]

This PR updates mypy from 1.17.1 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.

1.18.2

- Fix crash on recursive alias (Ivan Levkivskyi, PR [19845](https://github.com/python/mypy/pull/19845))
- Add additional guidance for stubtest errors when runtime is `object.__init__` (Stephen Morton, PR [19733](https://github.com/python/mypy/pull/19733))
- Fix handling of None values in f-string expressions in mypyc (BobTheBuidler, PR [19846](https://github.com/python/mypy/pull/19846))

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.

1.18.1

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

Links

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