The Mypy Blog: August 2023

We’ve just uploaded mypy 1.5 to the Python Package Index (PyPI). Mypy is a static type checker for Python. This release includes new features, deprecations 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.

Drop Support for Python 3.7

Mypy no longer supports running with Python 3.7, which has reached end-of-life. This was contributed by Shantanu (PR 15566).

Optional Check to Require Explicit @override

If you enable the explicit-override error code, mypy will generate an error if a method override doesn’t use the @typing.override decorator (as discussed in PEP 698). This way mypy will detect accidentally introduced overrides. Example:

    # mypy: enable-error-code="explicit-override"
    
    from typing_extensions import override
    
    class C:
        def foo(self) -> None: pass
        def bar(self) -> None: pass
    
    class D(C):
        # Error: Method "foo" is not using @override but is 
        # overriding a method
        def foo(self) -> None:
            ...
    
        @override
        def bar(self) -> None:  # OK
            ...

You can enable the error code via --enable-error-code=explicit-override on the mypy command line or enable_error_code = explicit-override in the mypy config file.

The override decorator will be available in typing in Python 3.12, but you can also use the backport from a recent version of typing_extensions on all supported Python versions.

This feature was contributed by Marc Mueller(PR 15512).

More Flexible TypedDict Creation and Update

Mypy was previously overly strict when type checking TypedDict creation and update operations. Though these checks were often technically correct, they sometimes triggered for apparently valid code. These checks have now been relaxed by default. You can enable stricter checking by using the new --extra-checks flag.

Construction using the ** syntax is now more flexible:

    from typing import TypedDict
    
    class A(TypedDict):
        foo: int
        bar: int
    
    class B(TypedDict):
        foo: int
    
    a: A = {"foo": 1, "bar": 2}
    b: B = {"foo": 3}
    a2: A = { **a, **b}  # OK (previously an error)

You can also call update() with a TypedDict argument that contains a subset of the keys in the updated TypedDict:

    a.update(b)  # OK (previously an error)

This feature was contributed by Ivan Levkivskyi (PR 15425).

Deprecated Flag: `--strict-concatenate`

The behavior of --strict-concatenate is now included in the new --extra-checks flag, and the old flag is deprecated.

Optionally Show Links to Error Code Documentation

If you use --show-error-code-links, mypy will add documentation links to (many) reported errors. The links are not shown for error messages that are sufficiently obvious, and they are shown once per error code only.

Example output:

    a.py:1: error: Need type annotation for "foo" (hint: "x: List[<type>] = ...")  [var-annotated]
    a.py:1: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-var-annotated for more info

This was contributed by Ivan Levkivskyi (PR 15449).

Consistently Avoid Type Checking Unreachable Code

If a module top level has unreachable code, mypy won’t type check the unreachable statements. This is consistent with how functions behave. The behavior of --warn-unreachable is also more consistent now.

This was contributed by Ilya Priven (PR 15386).

Experimental Improved Type Inference for Generic Functions

You can use --new-type-inference to opt into an experimental new type inference algorithm. It fixes issues when calling a generic functions with an argument that is also a generic function, in particular. This current implementation is still incomplete, but we encourage trying it out and reporting bugs if you encounter regressions. We are planning to enable the new algorithm by default in a future mypy release.

This feature was contributed by Ivan Levkivskyi (PR 15287).

Partial Support for Python 3.12

Mypy and mypyc now support running on recent Python 3.12 development versions. Not all new Python 3.12 features are supported, and we don’t ship compiled wheels for Python 3.12 yet.

Fix ast warnings for Python 3.12 (Nikita Sobolev, PR 15558)
mypyc: Fix multiple inheritance with a protocol on Python 3.12 (Jukka Lehtosalo, PR 15572)
mypyc: Fix self-compilation on Python 3.12 (Jukka Lehtosalo, PR 15582)
mypyc: Fix 3.12 issue with pickling of instances with __dict__ (Jukka Lehtosalo, PR 15574)
mypyc: Fix i16 on Python 3.12 (Jukka Lehtosalo, PR 15510)
mypyc: Fix int operations on Python 3.12 (Jukka Lehtosalo, PR 15470)
mypyc: Fix generators on Python 3.12 (Jukka Lehtosalo, PR 15472)
mypyc: Fix classes with __dict__ on 3.12 (Jukka Lehtosalo, PR 15471)
mypyc: Fix coroutines on Python 3.12 (Jukka Lehtosalo, PR 15469)
mypyc: Don't use _PyErr_ChainExceptions on 3.12, since it's deprecated (Jukka Lehtosalo, PR 15468)
mypyc: Add Python 3.12 feature macro (Jukka Lehtosalo, PR 15465)

Improvements to Dataclasses

Improve signature of dataclasses.replace (Ilya Priven, PR 14849)
Fix dataclass/protocol crash on joining types (Ilya Priven, PR 15629)
Fix strict optional handling in dataclasses (Ivan Levkivskyi, PR 15571)
Support optional types for custom dataclass descriptors (Marc Mueller, PR 15628)
Add __slots__ attribute to dataclasses (Nikita Sobolev, PR 15649)
Support better __post_init__ method signature for dataclasses (Nikita Sobolev, PR 15503)

Mypyc Improvements

Support unsigned 8-bit native integer type: mypy_extensions.u8 (Jukka Lehtosalo, PR 15564)
Support signed 16-bit native integer type: mypy_extensions.i16 (Jukka Lehtosalo, PR 15464)
Define mypy_extensions.i16 in stubs (Jukka Lehtosalo, PR 15562)
Document more unsupported features and update supported features (Richard Si, PR 15524)
Fix final NamedTuple classes (Richard Si, PR 15513)
Use C99 compound literals for undefined tuple values (Jukka Lehtosalo, PR 15453)
Don't explicitly assign NULL values in setup functions (Logan Hunt, PR 15379)

Stubgen Improvements

Teach stubgen to work with complex and unary expressions (Nikita Sobolev, PR 15661)
Support ParamSpec and TypeVarTuple (Ali Hamdan, PR 15626)
Fix crash on non-str docstring (Ali Hamdan, PR 15623)

Documentation Updates

Add documentation for additional error codes (Ivan Levkivskyi, PR 15539)
Improve documentation of type narrowing (Ilya Priven, PR 15652)
Small improvements to protocol documentation (Shantanu, PR 15460)
Remove confusing instance variable example in cheat sheet (Adel Atallah, PR 15441)

Other Notable Fixes and Improvements

Constant fold additional unary and binary expressions (Richard Si, PR 15202)
Exclude the same special attributes from Protocol as CPython (Kyle Benesch, PR 15490)
Change the default value of the slots argument of attrs.define to True, to match runtime behavior (Ilya Priven, PR 15642)
Fix type of class attribute if attribute is defined in both class and metaclass (Alex Waygood, PR 14988)
Handle type the same as typing.Type in the first argument of classmethods (Erik Kemperman, PR 15297)
Fix --find-occurrences flag (Shantanu, PR 15528)
Fix error location for class patterns (Nikita Sobolev, PR 15506)
Fix re-added file with errors in mypy daemon (Ivan Levkivskyi, PR 15440)
Fix dmypy run on Windows (Ivan Levkivskyi, PR 15429)
Fix abstract and non-abstract variant error for property deleter (Shantanu, PR 15395)
Remove special casing for "cannot" in error messages (Ilya Priven, PR 15428)
Add runtime __slots__ attribute to attrs classes (Nikita Sobolev, PR 15651)
Add get_expression_type to CheckerPluginInterface (Ilya Priven, PR 15369)
Remove parameters that no longer exist from NamedTuple._make() (Alex Waygood, PR 15578)
Allow using typing.Self in __new__ with an explicit @staticmethod decorator (Erik Kemperman, PR 15353)
Fix self types in subclass methods without Self annotation (Ivan Levkivskyi, PR 15541)
Check for abstract class objects in tuples (Nikita Sobolev, PR 15366)

Typeshed Updates

Typeshed is now modular and distributed as separate PyPI packages for everything except the standard library stubs. Please see git log for full list of typeshed changes.

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

Adel Atallah
Alex Waygood
Ali Hamdan
Erik Kemperman
Federico Padua
Ilya Priven
Ivan Levkivskyi
Jelle Zijlstra
Jared Hance
Jukka Lehtosalo
Kyle Benesch
Logan Hunt
Marc Mueller
Nikita Sobolev
Richard Si
Shantanu
Stavros Ntentos
Valentin Stanciu

The Mypy Blog

Thursday, 10 August 2023

Mypy 1.5 Released

Drop Support for Python 3.7

Optional Check to Require Explicit @override

More Flexible TypedDict Creation and Update

Deprecated Flag: `--strict-concatenate`

Optionally Show Links to Error Code Documentation

Consistently Avoid Type Checking Unreachable Code

Experimental Improved Type Inference for Generic Functions

Partial Support for Python 3.12

Improvements to Dataclasses

Mypyc Improvements

Stubgen Improvements

Documentation Updates

Other Notable Fixes and Improvements

Typeshed Updates

Acknowledgements

Contributors

Thursday, 10 August 2023

Mypy 1.5 Released

Drop Support for Python 3.7

Optional Check to Require Explicit @override

More Flexible TypedDict Creation and Update

Deprecated Flag: --strict-concatenate

Optionally Show Links to Error Code Documentation

Consistently Avoid Type Checking Unreachable Code

Experimental Improved Type Inference for Generic Functions

Partial Support for Python 3.12

Improvements to Dataclasses

Mypyc Improvements

Stubgen Improvements

Documentation Updates

Other Notable Fixes and Improvements

Typeshed Updates

Acknowledgements

Deprecated Flag: `--strict-concatenate`