Friday, 20 December 2024

Mypy 1.14 Released

We’ve just uploaded mypy 1.14 to the Python Package Index (PyPI).

Mypy is a static type checker for Python. This release includes new features 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.

Change to Enum Membership Semantics

As per the updated typing specification for enums, enum members must be left unannotated. 

class Pet(Enum):
    CAT = 1  # Member attribute
    DOG = 2  # Member attribute

    # New error: Enum members must be left unannotated
    WOLF: int = 3

    species: str  # Considered a non-member attribute

In particular, the specification change can result in issues in type stubs (.pyi files), since historically it was common to leave the value absent: 

# In a type stub (.pyi file)

class Pet(Enum):
    # Change in semantics: previously considered members,
    # now non-member attributes
    CAT: int
    DOG: int

    # Mypy will now issue a warning if it detects this
    # situation in type stubs:
    # > Detected enum "Pet" in a type stub with zero
    # > members. There is a chance this is due to a recent
    # > change in the semantics of enum membership. If so,
    # > use member = value to mark an enum member,
    # > instead of member: type

class Pet(Enum):
    # As per the specification, you should now do one of
    # the following:
    DOG = 1  # Member attribute with value 1 and known type
    WOLF = cast(int, ...)  # Member attribute with unknown
                           # value but known type
    LION = ...  # Member attribute with unknown value and
                # unknown type

Contributed by Terence Honles (PR 17207) and

Shantanu Jain (PR 18068).

Support for @deprecated Decorator (PEP 702)

Mypy can now issue errors or notes when code imports a deprecated feature explicitly with a from mod import depr statement, or uses a deprecated feature imported otherwise or defined locally. Features are considered deprecated when decorated with warnings.deprecated, as specified in PEP 702.

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

Use the command line flag --report-deprecated-as-note or config file option report_deprecated_as_note=True to turn all such errors into notes.

Deprecation errors will be enabled by default in a future mypy version.

This feature was contributed by Christoph Tyralla.

List of changes:

  • Add basic support for PEP 702 (@deprecated) (Christoph Tyralla, PR 17476)
  • Support descriptors with @deprecated (Christoph Tyralla, PR 18090)
  • Make "deprecated" note an error, disabled by default (Valentin Stanciu, PR 18192)
  • Consider all possible type positions with @deprecated (Christoph Tyralla, PR 17926)
  • Improve the handling of explicit type annotations in assignment statements with @deprecated (Christoph Tyralla, PR 17899)

Optionally Analyzing Untyped Modules

Mypy normally doesn't analyze imports from third-party modules (installed using pip, for example) if there are no stubs or a py.typed marker file. To force mypy to analyze these imports, you can now use the --follow-untyped-imports flag or set the follow_untyped_imports config file option to True. This can be set either in the global section of your mypy config file, or individually on a per-module basis.

This feature was contributed by Jannick Kremer.

List of changes:

  • Implement flag to allow type checking of untyped modules (Jannick Kremer, PR 17712)
  • Warn about --follow-untyped-imports (Shantanu, PR 18249)

Support New Style Type Variable Defaults (PEP 696)

Mypy now supports type variable defaults using the new syntax described in PEP 696, which was introduced in Python 3.13. Example: 

@dataclass
class Box[T = int]:  # Set default for "T"
    value: T | None = None

reveal_type(Box())                      # type is Box[int], since it's the default
reveal_type(Box(value="Hello World!"))  # type is Box[str]

This feature was contributed by Marc Mueller (PR 17985).

Improved For Loop Index Variable Type Narrowing

Mypy now preserves the literal type of for loop index variables, to support TypedDict lookups. Example: 

from typing import TypedDict

class X(TypedDict):
    hourly: int
    daily: int

def func(x: X) -> int:
    s = 0
    for var in ("hourly", "daily"):
        # "Union[Literal['hourly']?, Literal['daily']?]"
        reveal_type(var)

        # x[var] no longer triggers a literal-required error
        s += x[var]
    return s

This was contributed by Marc Mueller (PR 18014).

Mypyc Improvements

  • Document optimized bytes operations and additional str operations (Jukka Lehtosalo, PR 18242)
  • Add primitives and specialization for ord() (Jukka Lehtosalo, PR 18240)
  • Optimize str.encode with specializations for common used encodings (Valentin Stanciu, PR 18232)
  • Fix fall back to generic operation for staticmethod and classmethod (Advait Dixit, PR 18228)
  • Support unicode surrogates in string literals (Jukka Lehtosalo, PR 18209)
  • Fix index variable in for loop with builtins.enumerate (Advait Dixit, PR 18202)
  • Fix check for enum classes (Advait Dixit, PR 18178)
  • Fix loading type from imported modules (Advait Dixit, PR 18158)
  • Fix initializers of final attributes in class body (Jared Hance, PR 18031)
  • Fix name generation for modules with similar full names (aatle, PR 18001)
  • Fix relative imports in __init__.py (Shantanu, PR 17979)
  • Optimize dunder methods (jairov4, PR 17934)
  • Replace deprecated _PyDict_GetItemStringWithError (Marc Mueller, PR 17930)
  • Fix wheel build for cp313-win (Marc Mueller, PR 17941)
  • Use public PyGen_GetCode instead of vendored implementation (Marc Mueller, PR 17931)
  • Optimize calls to final classes (jairov4, PR 17886)
  • Support ellipsis (...) expressions in class bodies (Newbyte, PR 17923)
  • Sync pythoncapi_compat.h (Marc Mueller, PR 17929)
  • Add runtests.py mypyc-fast for running fast mypyc tests (Jukka Lehtosalo, PR 17906)

Stubgen Improvements

  • Do not include mypy generated symbols (Ali Hamdan, PR 18137)
  • Fix FunctionContext.fullname for nested classes (Chad Dombrova, PR 17963)
  • Add flagfile support (Ruslan Sayfutdinov, PR 18061)
  • Add support for PEP 695 and PEP 696 syntax (Ali Hamdan, PR 18054)

Stubtest Improvements

  • Allow the use of --show-traceback and --pdb with stubtest (Stephen Morton, PR 18037)
  • Verify __all__ exists in stub (Sebastian Rittau, PR 18005)
  • Stop telling people to use double underscores (Jelle Zijlstra, PR 17897)

Documentation Updates

  • Update config file documentation (sobolevn, PR 18103)
  • Improve contributor documentation for Windows (ag-tafe, PR 18097)
  • Correct note about --disallow-any-generics flag in documentation (Abel Sen, PR 18055)
  • Further caution against --follow-imports=skip (Shantanu, PR 18048)
  • Fix the edit page buttton link in documentation (Kanishk Pachauri, PR 17933)

Other Notables Fixes and Improvements

  • Show Protocol __call__ for arguments with incompatible types (MechanicalConstruct, PR 18214)
  • Make join and meet symmetric with strict_optional (MechanicalConstruct, PR 18227)
  • Preserve block unreachablility when checking function definitions with constrained TypeVars (Brian Schubert, PR 18217)
  • Do not include non-init fields in the synthesized __replace__ method for dataclasses (Victorien, PR 18221)
  • Disallow TypeVar constraints parameterized by type variables (Brian Schubert, PR 18186)
  • Always complain about invalid varargs and varkwargs (Shantanu, PR 18207)
  • Set default strict_optional state to True (Shantanu, PR 18198)
  • Preserve type variable default None in type alias (Sukhorosov Aleksey, PR 18197)
  • Add checks for invalid usage of continue/break/return in except* block (coldwolverine, PR 18132)
  • Do not consider bare TypeVar not overlapping with None for reachability analysis (Stanislav Terliakov, PR 18138)
  • Special case types.DynamicClassAttribute as property-like (Stephen Morton, PR 18150)
  • Disallow bare ParamSpec in type aliases (Brian Schubert, PR 18174)
  • Move long_description metadata to pyproject.toml (Marc Mueller, PR 18172)
  • Support ==-based narrowing of Optional (Christoph Tyralla, PR 18163)
  • Allow TypedDict assignment of Required item to NotRequired ReadOnly item (Brian Schubert, PR 18164)
  • Allow nesting of Annotated with TypedDict special forms inside TypedDicts (Brian Schubert, PR 18165)
  • Infer generic type arguments for slice expressions (Brian Schubert, PR 18160)
  • Fix checking of match sequence pattern against bounded type variables (Brian Schubert, PR 18091)
  • Fix incorrect truthyness for Enum types and literals (David Salvisberg, PR 17337)
  • Move static project metadata to pyproject.toml (Marc Mueller, PR 18146)
  • Fallback to stdlib json if integer exceeds 64-bit range (q0w, PR 18148)
  • Fix 'or' pattern structural matching exhaustiveness (yihong, PR 18119)
  • Fix type inference of positional parameter in class pattern involving builtin subtype (Brian Schubert, PR 18141)
  • Fix [override] error with no line number when argument node has no line number (Brian Schubert, PR 18122)
  • Fix some dmypy crashes (Ivan Levkivskyi, PR 18098)
  • Fix subtyping between instance type and overloaded (Shantanu, PR 18102)
  • Clean up new_semantic_analyzer config (Shantanu, PR 18071)
  • Issue warning for enum with no members in stub (Shantanu, PR 18068)
  • Fix enum attributes are not members (Terence Honles, PR 17207)
  • Fix crash when checking slice expression with step 0 in tuple index (Brian Schubert, PR 18063)
  • Allow union-with-callable attributes to be overridden by methods (Brian Schubert, PR 18018)
  • Emit [mutable-override] for covariant override of attribute with method (Brian Schubert, PR 18058)
  • Support ParamSpec mapping with functools.partial (Stanislav Terliakov, PR 17355)
  • Fix approved stub ignore, remove normpath (Shantanu, PR 18045)
  • Make disallow-any-unimported flag invertible (Séamus Ó Ceanainn, PR 18030)
  • Filter to possible package paths before trying to resolve a module (falsedrow, PR 18038)
  • Fix overlap check for ParamSpec types (Jukka Lehtosalo, PR 18040)
  • Do not prioritize ParamSpec signatures during overload resolution (Stanislav Terliakov, PR 18033)
  • Fix ternary union for literals (Ivan Levkivskyi, PR 18023)
  • Fix compatibility checks for conditional function definitions using decorators (Brian Schubert, PR 18020)
  • TypeGuard should be bool not Any when matching TypeVar (Evgeniy Slobodkin, PR 17145)
  • Fix convert-cache tool (Shantanu, PR 17974)
  • Fix generator comprehension with mypyc (Shantanu, PR 17969)
  • Fix crash issue when using shadowfile with pretty (Max Chang, PR 17894)
  • Fix multiple nested classes with new generics syntax (Max Chang, PR 17820)
  • Better error for mypy -p package without py.typed (Joe Gordon, PR 17908)
  • Emit error for raise NotImplemented (Brian Schubert, PR 17890)
  • Add is_lvalue attribute to AttributeContext (Brian Schubert, PR 17881)

Acknowledgements

Thanks to all mypy contributors who contributed to this release:

  • aatle
  • Abel Sen
  • Advait Dixit
  • ag-tafe
  • Alex Waygood
  • Ali Hamdan
  • Brian Schubert
  • Carlton Gibson
  • Chad Dombrova
  • Chelsea Durazo
  • chiri
  • Christoph Tyralla
  • coldwolverine
  • David Salvisberg
  • Ekin Dursun
  • Evgeniy Slobodkin
  • falsedrow
  • Gaurav Giri
  • Ihor
  • Ivan Levkivskyi
  • jairov4
  • Jannick Kremer
  • Jared Hance
  • Jelle Zijlstra
  • jianghuyiyuan
  • Joe Gordon
  • John Doknjas
  • Jukka Lehtosalo
  • Kanishk Pachauri
  • Marc Mueller
  • Max Chang
  • MechanicalConstruct
  • Newbyte
  • q0w
  • Ruslan Sayfutdinov
  • Sebastian Rittau
  • Shantanu
  • sobolevn
  • Stanislav Terliakov
  • Stephen Morton
  • Sukhorosov Aleksey
  • Séamus Ó Ceanainn
  • Terence Honles
  • Valentin Stanciu
  • vasiliy
  • Victorien
  • yihong

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

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