We’ve just uploaded mypy 1.8 to the Python Package Index (PyPI). 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.
Type-checking Improvements
Do not intersect types in isinstance checks if at least one is final (Christoph Tyralla, PR 16330)
Detect that @final class without __bool__ cannot have falsey instances (Ilya Priven, PR 16566)
Do not allow TypedDict classes with extra keywords (Nikita Sobolev, PR 16438)
Do not allow class-level keywords for NamedTuple (Nikita Sobolev, PR 16526)
Make imprecise constraints handling more robust (Ivan Levkivskyi, PR 16502)
Fix strict-optional in extending generic TypedDict (Ivan Levkivskyi, PR 16398)
Allow type ignores of PEP 695 constructs (Shantanu, PR 16608)
Enable type_check_only support for TypedDict and NamedTuple (Nikita Sobolev, PR 16469)
Performance Improvements
Add fast path to analyzing special form assignments (Jukka Lehtosalo, PR 16561)
Improvements to Error Reporting
Don't show documentation links for plugin error codes (Ivan Levkivskyi, PR 16383)
Improve error messages for super checks and add more tests (Nikita Sobolev, PR 16393)
We’ve just uploaded mypy 1.7 to the Python Package Index (PyPI). 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.
Using TypedDict for **kwargs Typing
Mypy now has support for using Unpack[...] with a TypedDict type to annotate **kwargs arguments enabled by default. Example:
# Or 'from typing_extensions import ...'
from typing import TypedDict, Unpack
class Person(TypedDict):
name: str
age: int
def foo(**kwargs: Unpack[Person]) -> None:
...
foo(name="x", age=1) # Ok
foo(name=1) # Error
The definition of foo above is equivalent to the one below, with keyword-only arguments name and age:
def foo(*, name: str, age: int) -> None:
...
Refer to PEP 692 for more information. Note that unlike in the current version of the PEP, mypy always treats signatures with Unpack[SomeTypedDict] as equivalent to their expanded forms with explicit keyword arguments, and there aren't special type checking rules for TypedDict arguments.
This was contributed by Ivan Levkivskyi back in 2022 (PR 13471).
TypeVarTuple Support Enabled (Experimental)
Mypy now has support for variadic generics (TypeVarTuple) enabled by default, as an experimental feature. Refer to PEP 646 for the details.
TypeVarTuple was implemented by Jared Hance and Ivan Levkivskyi over several mypy releases, with help from Jukka Lehtosalo.
Changes included in this release:
Fix handling of tuple type context with unpacks (Ivan Levkivskyi, PR 16444)
Handle TypeVarTuples when checking overload constraints (robjhornby, PR 16428)
Enable Unpack/TypeVarTuple support (Ivan Levkivskyi, PR 16354)
Fix crash on unpack call special-casing (Ivan Levkivskyi, PR 16381)
Some final touches for variadic types support (Ivan Levkivskyi, PR 16334)
Support PEP-646 and PEP-692 in the same callable (Ivan Levkivskyi, PR 16294)
Support new * syntax for variadic types (Ivan Levkivskyi, PR 16242)
Correctly handle runtime type applications of variadic types (Ivan Levkivskyi, PR 16240)
Support variadic tuple packing/unpacking (Ivan Levkivskyi, PR 16205)
Better support for variadic calls and indexing (Ivan Levkivskyi, PR 16131)
Subtyping and inference of user-defined variadic types (Ivan Levkivskyi, PR 16076)
Complete type analysis of variadic types (Ivan Levkivskyi, PR 15991)
New Way of Installing Mypyc Dependencies
If you want to install package dependencies needed by mypyc (not just mypy), you should now install mypy[mypyc] instead of just mypy:
python3 -m pip install -U 'mypy[mypyc]'
Mypy has many more users than mypyc, so always installing mypyc dependencies would often bring unnecessary dependencies.
This change was contributed by Shantanu (PR 16229).
New Rules for Re-exports
Mypy no longer considers an import such as import a.b as b as an explicit re-export. The old behavior was arguably inconsistent and surprising. This may impact some stub packages, such as older versions of types-six. You can change the import to from a import b as b, if treating the import as a re-export was intentional.
This change was contributed by Anders Kaseorg (PR 14086).
Improved Type Inference
The new type inference algorithm that was recently introduced to mypy (but was not enabled by default) is now enabled by default. It improves type inference of calls to generic callables where an argument is also a generic callable, in particular. You can use --old-type-inference to disable the new behavior.
The new algorithm can (rarely) produce different error messages, different error codes, or errors reported on different lines. This is more likely in cases where generic types were used incorrectly.
The new type inference algorithm was contributed by Ivan Levkivskyi. PR 16345 enabled it by default.
Narrowing Tuple Types Using len()
Mypy now can narrow tuple types using len() checks. Example:
def f(t: tuple[int, int] | tuple[int, int, int]) -> None:
if len(t) == 2:
a, b = t # Ok
...
This feature was contributed by Ivan Levkivskyi (PR 16237).
More Precise Tuple Lengths (Experimental)
Mypy supports experimental, more precise checking of tuple type lengths through --enable-incomplete-feature=PreciseTupleTypes. Refer to the documentation for more information.
More generally, we are planning to use --enable-incomplete-feature to introduce experimental features that would benefit from community feedback.
This feature was contributed by Ivan Levkivskyi (PR 16237).
Mypy Changelog
We now maintain a changelog in the mypy Git repository. It mirrors the contents of mypy release blog posts. We will continue to also publish release blog posts. In the future, release blog posts will be created based on the changelog near a release date.
We’ve just uploaded mypy 1.6 to the Python Package Index (PyPI). 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.
Introduce Error Subcodes for Import Errors
Mypy now uses the error code import-untyped if an import targets an installed library that doesn’t support static type checking, and no stub files are available. Other invalid imports produce the import-not-found error code. They both are subcodes of the import error code, which was previously used for both kinds of import-related errors.
Use --disable-error-code=import-untyped to only ignore import errors about installed libraries without stubs. This way mypy will still report errors about typos in import statements, for example.
If you use --warn-unused-ignore or --strict, mypy will complain if you use # type: ignore[import] to ignore an import error. You are expected to use one of the more specific error codes instead. Otherwise, ignoring the import error code continues to silence both errors.
This feature was contributed by Shantanu (PR 15840, PR 14740).
Remove Support for Targeting Python 3.6 and Earlier
Running mypy with --python-version 3.6, for example, is no longer supported. Python 3.6 hasn’t been properly supported by mypy for some time now, and this makes it explicit. This was contributed by Nikita Sobolev (PR 15668).
Selective Filtering of --disallow-untyped-calls Targets
Using --disallow-untyped-calls could be annoying when using libraries with missing type information, as mypy would generate many errors about code that uses the library. Now you can use --untyped-calls-exclude=acme, for example, to disable these errors about calls targeting functions defined in the acme package. Refer to the documentation for more information.
This feature was contributed by Ivan Levkivskyi (PR 15845).
Improved Type Inference between Callable Types
Mypy now does a better job inferring type variables inside arguments of callable types. For example, this code fragment now type checks correctly:
Previously mypy would generate an error about the definition of f above. This is slightly unsafe if the upper bound of T is object, since the value of the type variable could be None. We relaxed the rules a little, since this solves a common issue.
This feature was contributed by Ivan Levkivskyi (PR 15846).
Improvements to --new-type-inference
The experimental new type inference algorithm (polymorphic inference) introduced as an opt-in feature in mypy 1.5 has several improvements:
Fix type narrowing of == None and in (None,) conditions (Marti Raudsepp, PR 15760)
Fix inference for attrs.fields (Shantanu, PR 15688)
Make “await in non-async function” a non-blocking error and give it an error code (Gregory Santosa, PR 15384)
Add basic support for decorated overloads (Ivan Levkivskyi, PR 15898)
Fix TypeVar regression with self types (Ivan Levkivskyi, PR 15945)
Add __match_args__ to dataclasses with no fields (Ali Hamdan, PR 15749)
Include stdout and stderr in dmypy verbose output (Valentin Stanciu, PR 15881)
Improve match narrowing and reachability analysis (Shantanu, PR 15882)
Support __bool__ with Literal in --warn-unreachable (Jannic Warken, PR 15645)
Fix inheriting from generic @frozen attrs class (Ilya Priven, PR 15700)
Correctly narrow types for tuple[type[X], ...] (Nikita Sobolev, PR 15691)
Don't flag intentionally empty generators unreachable (Ilya Priven, PR 15722)
Add tox.ini to mypy sdist (Marcel Telka, PR 15853)
Fix mypyc regression with pretty (Shantanu, PR 16124)
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 Max Murin, who did most of the release manager work for this release (I just did
the final steps).
Thanks to all mypy contributors who contributed to this release:
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.
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)
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:
We’ve just uploaded mypy 1.4 to the Python Package Index (PyPI). 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.
The Override Decorator
Mypy can now ensure that when renaming a method, overrides are also renamed. You can explicitly mark a method as overriding a base class method by using the @typing.override decorator (PEP 698). If the method is then renamed in the base class while the method override is not, mypy will generate an error. The 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 byThomas M Kehrenberg (PR 14609).
Propagating Type Narrowing to Nested Functions
Previously, type narrowing was not propagated to nested functions because it would not be sound if the narrowed variable changed between the definition of the nested function and the call site. Mypy will now propagate the narrowed type if the variable is not assigned to after the definition of the nested function:
def outer(x: str | None = None) -> None:
if x is None:
x = calculate_default()
reveal_type(x) # "str" (narrowed)
def nested() -> None:
reveal_type(x) # Now "str" (used to be "str | None")
nested()
This may generate some new errors because asserts that were previously necessary may become tautological or no-ops.
This was contributed by Jukka Lehtosalo (PR 15133).
Narrowing Enum Values Using “==”
Mypy now allows narrowing enum types using the == operator. Previously this was only supported when using the is operator. This makes exhaustiveness checking with enum types more usable, as the requirement to use the is operator was not very intuitive. In this example mypy can detect that the developer forgot to handle the value MyEnum.C in example
from enum import Enum
class MyEnum(Enum):
A = 0
B = 1
C = 2
def example(e: MyEnum) -> str: # Error: Missing return statement
if e == MyEnum.A:
return 'x'
elif e == MyEnum.B:
return 'y'
Adding an extra elif case resolves the error:
...
def example(e: MyEnum) -> str: # No error -- all values covered
if e == MyEnum.A:
return 'x'
elif e == MyEnum.B:
return 'y'
elif e == MyEnum.C:
return 'z'
This change can cause false positives in test cases that have assert statements like assert o.x == SomeEnum.X when using --strict-equality. Example:
# mypy: strict-equality
from enum import Enum
class MyEnum(Enum):
A = 0
B = 1
class C:
x: MyEnum
...
def test_something() -> None:
c = C(...)
assert c.x == MyEnum.A
c.do_something_that_changes_x()
assert c.x == MyEnum.B # Error: Non-overlapping equality check
These errors can be ignored using # type: ignore[comparison-overlap], or you can perform the assertion using a temporary variable as a workaround:
...
def test_something() -> None:
...
x = c.x
assert x == MyEnum.A # Does not narrow c.x
c.do_something_that_changes_x()
x = c.x
assert x == MyEnum.B # OK
This feature was contributed by Shantanu (PR 11521).
Performance Improvements
Speed up simplification of large union types and also fix a recursive tuple crash (Shantanu, PR 15128)
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:
Adrian Garcia Badaracco
AJ Rasmussen
Alan Du
Alex Waygood
Ali Hamdan
Carl Karsten
dosisod
Ethan Smith
Gregory Santosa
Heather White
Henrik Bäärnhielm
Ilya Konstantinov
Ilya Priven
Ivan Levkivskyi
Juhi Chandalia
Jukka Lehtosalo
Logan Hunt
madt2709
Marc Mueller
Max Murin
Nikita Sobolev
Omar Silva
Özgür
Richard Si
Rohit Sanjay
Shantanu
teresa0605
Thomas M Kehrenberg
Tin Tvrtković
Tushar Sadhwani
Valentin Stanciu
Viicos
Vincent Vanlaer
Wesley Collin Wright
William Santosa
yaegassy
I’d also like to thank my employer, Dropbox, for supporting mypy development.
We’ve just uploaded mypy 1.3 to the Python Package Index (PyPI). 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.
Performance Improvements
Improve performance of union subtyping (Shantanu, PR 15104)
Fix unions of bools and ints (Tomer Chachamu, PR 15066)
Other Fixes and Improvements
Fix narrowing union types that include Self with isinstance (Christoph Tyralla, PR 14923)
Allow objects matching SupportsKeysAndGetItem to be unpacked (Bryan Forbes, PR 14990)
Check type guard validity for staticmethods (EXPLOSION, PR 14953)
Fix sys.platform when cross-compiling with emscripten (Ethan Smith, PR 14888)
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:
We’ve just uploaded mypy 1.2 to the Python Package Index (PyPI). 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.
Improvements to Dataclass Transforms
Support implicit default for "init" parameter in field specifiers (Wesley Collin Wright and Jukka Lehtosalo, PR 15010)
Support descriptors in dataclass transform (Jukka Lehtosalo, PR 15006)
Fix frozen_default in incremental mode (Wesley Collin Wright)
Fix frozen behavior for base classes with direct metaclasses (Wesley Collin Wright, PR 14878)
Mypyc: Native Floats
Mypyc now uses a native, unboxed representation for values of type float. Previously these were heap-allocated Python objects. Native floats are faster and use less memory. Code that uses floating-point operations heavily can be several times faster when using native floats.
Various float operations and math functions also now have optimized implementations. Refer to the documentation for a full list.
This can change the behavior of existing code that uses subclasses of float. When assigning an instance of a subclass of float to a variable with the float type, it gets implicitly converted to a float instance when compiled:
from lib import MyFloat # MyFloat ia a subclass of "float"
def example() -> None:
x = MyFloat(1.5)
y: float = x # Implicit conversion from MyFloat to float
print(type(y)) # float, not MyFloat
Previously, implicit conversions were applied to int subclasses but not float subclasses.
Also, int values can no longer be assigned to a variable with type float in compiled code, since these types now have incompatible representations. An explicit conversion is required:
def example(n: int) -> None:
a: float = 1 # Error: cannot assign "int" to "float"
b: float = 1.0 # OK
c: float = n # Error
d: float = float(n) # OK
This restriction only applies to assignments, since they could otherwise narrow down the type of a variable from float to int. int values can still be implicitly converted to float when passed as arguments to functions that expect float values.
Note that mypyc still doesn’t support arrays of unboxed float values. Using list[float] involves heap-allocated float objects, since list can only store boxed values. Support for efficient floating point arrays is one of the next major planned mypyc features.
Related changes:
Use a native unboxed representation for floats (Jukka Lehtosalo, PR 14880)
Document native floats and integers (Jukka Lehtosalo, PR 14927)
Fixes to float to int conversion (Jukka Lehtosalo, PR 14936)
Mypyc: Native Integers
Mypyc now supports signed 32-bit and 64-bit integer types in addition to the arbitrary-precision int type. You can use the types mypy_extensions.i32 and mypy_extensions.i64 to speed up code that uses integer operations heavily.
Simple example:
from mypy_extensions import i64
def inc(x: i64) -> i64:
return x + 1
Refer to the documentation for more information. This feature was contributed by Jukka Lehtosalo.
Other Mypyc Fixes and Improvements
Support iterating over a TypedDict (Richard Si, PR 14747)
Faster coercions between different tuple types (Jukka Lehtosalo, PR 14899)
Faster calls via type aliases (Jukka Lehtosalo, PR 14784)
Faster classmethod calls via cls (Jukka Lehtosalo, PR 14789)
Fixes to Crashes
Fix crash on class-level import in protocol definition (Ivan Levkivskyi, PR 14926)
Fix crash on single item union of alias (Ivan Levkivskyi, PR 14876)
Fix crash on ParamSpec in incremental mode (Ivan Levkivskyi, PR 14885)
Documentation Updates
Update adopting --strict documentation for 1.0 (Shantanu, PR 14865)
Some minor documentation tweaks (Jukka Lehtosalo, PR 14847)
Improve documentation of top level mypy: disable-error-code comment (Nikita Sobolev, PR 14810)
Error Reporting Improvements
Add error code to typing_extensions suggestion (Shantanu, PR 14881)
Add a separate error code for top-level await (Nikita Sobolev, PR 14801)
Don’t suggest two obsolete stub packages (Jelle Zijlstra, PR 14842)
Add suggestions for pandas-stubs and lxml-stubs (Shantanu, PR 14737)
Other Fixes and Improvements
Multiple inheritance considers callable objects as subtypes of functions (Christoph Tyralla, PR 14855)
stubtest: Respect @final runtime decorator and enforce it in stubs (Nikita Sobolev, PR 14922)
Fix false positives related to type[<type-var>] (sterliakov, PR 14756)
Fix duplication of ParamSpec prefixes and properly substitute ParamSpecs (EXPLOSION, PR 14677)
Fix line number if __iter__ is incorrectly reported as missing (Jukka Lehtosalo, PR 14893)
Fix incompatible overrides of overloaded generics with self types (Shantanu, PR 14882)
Allow SupportsIndex in slice expressions (Shantanu, PR 14738)
Support if statements in bodies of dataclasses and classes that use dataclass_transform (Jacek Chałupka, PR 14854)
Allow iterable class objects to be unpacked (including enums) (Alex Waygood, PR 14827)
Fix narrowing for walrus expressions used in match statements (Shantanu, PR 14844)
Add signature for attr.evolve (Ilya Konstantinov, PR 14526)
Fix Any inference when unpacking iterators that don't directly inherit from typing.Iterator (Alex Waygood, PR 14821)
Fix unpack with overloaded __iter__ method (Nikita Sobolev, PR 14817)
Reduce size of JSON data in mypy cache (dosisod, PR 14808)
Improve “used before definition” checks when a local definition has the same name as a global definition (Stas Ilinskiy, PR 14517)
Honor NoReturn as __setitem__ return type to mark unreachable code (sterliakov, PR 12572)
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:
We’ve just uploaded mypy 1.1.1 to the Python Package Index (PyPI). 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.
Support for dataclass_transform
This release adds full support for the dataclass_transform decorator defined in PEP 681. This allows decorators, base classes, and metaclasses that generate a __init__ method or other methods based on the properties of that class (similar to dataclasses) to have those methods recognized by mypy.
This was contributed by Wesley Collin Wright.
Dedicated Error Code for Method Assignments
Mypy can’t safely check all assignments to methods (a form of monkey patching), so mypy generates an error by default. To make it easier to ignore this error, mypy now uses the new error code method-assign for this. By disabling this error code in a file or globally, mypy will no longer complain about assignments to methods if the signatures are compatible.
Mypy also supports the old error code assignment for these assignments to prevent a backward compatibility break. More generally, we can use this mechanism in the future if we wish to split or rename another existing error code without causing backward compatibility issues.
This was contributed by Ivan Levkivskyi (PR 14570).
Fixes to Crashes
Fix a crash on walrus in comprehension at class scope (Ivan Levkivskyi, PR 14556)
Fix crash related to value-constrained TypeVar (Shantanu, PR 14642)
Check that type guards accept a positional argument (EXPLOSION, PR 14238)
Fix bug with in operator used with a union of Container and Iterable (Max Murin, PR 14384)
Support protocol inference for type[T] via metaclass (Ivan Levkivskyi, PR 14554)
Allow overlapping comparisons between bytes-like types (Shantanu, PR 14658)
Fix mypy daemon documentation link in README (Ivan Levkivskyi, PR 14644)
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:
Alex Waygood
Avasam
Chad Dombrova
dosisod
EXPLOSION
hamdanal
Ilya Konstantinov
Ivan Levkivskyi
Jared Hance
JoaquimEsteves
Jukka Lehtosalo
Marc Mueller
Max Murin
Michael Lee
Michael R. Crusoe
Richard Si
Rodrigo Silva
Shantanu
Stas Ilinskiy
Wesley Collin Wright
Yilei "Dolee" Yang
Yurii Karabas
We’d also like to thank our employer, Dropbox, for funding the mypy core team.
We’ve just uploaded mypy 1.0 to the Python Package Index (PyPI). 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.
New Release Versioning Scheme
Now that mypy reached 1.0, we’ll switch to a new versioning scheme. Mypy version numbers will be of form x.y.z.
Rules:
The major release number (x) is incremented if a feature release includes a significant backward incompatible change that affects a significant fraction of users.
The minor release number (y) is incremented on each feature release. Minor releases include updated stdlib stubs from typeshed.
The point release number (z) is incremented when there are fixes only.
Mypy doesn't use SemVer, since most minor releases have at least minor backward incompatible changes in typeshed, at the very least. Also, many type checking features find new legitimate issues in code. These are not considered backward incompatible changes, unless the number of new errors is very high.
Any significant backward incompatible change must be announced in the blog post for the previous feature release, before making the change. The previous release must also provide a flag to explicitly enable or disable the new behavior (whenever practical), so that users will be able to prepare for the changes and report issues. We should keep the feature flag for at least a few releases after we've switched the default.
Mypy 1.0 is up to 40% faster than mypy 0.991 when type checking the Dropbox internal codebase. We also set up a daily job to measure the performance of the most recent development version of mypy to make it easier to track changes in performance.
Many optimizations contributed to this improvement:
Improve performance for errors on class with many attributes (Shantanu, PR 14379)
Speed up make_simplified_union (Jukka Lehtosalo, PR 14370)
Some semantic analyzer micro-optimizations (Jukka Lehtosalo, PR 14367)
A few miscellaneous micro-optimizations (Jukka Lehtosalo, PR 14366)
Optimization: Avoid a few uses of contextmanagers in semantic analyzer (Jukka Lehtosalo, PR 14360)
Optimization: Enable always defined attributes in Type subclasses (Jukka Lehtosalo, PR 14356)
Optimization: Remove expensive context manager in type analyzer (Jukka Lehtosalo, PR 14357)
subtypes: fast path for Union/Union subtype check (Hugues, PR 14277)
Micro-optimization: avoid Bogus[int] types that cause needless boxing (Jukka Lehtosalo, PR 14354)
Avoid slow error message logic if errors not shown to user (Jukka Lehtosalo, PR 14336)
Speed up the implementation of hasattr() checks (Jukka Lehtosalo, PR 14333)
Avoid the use of a context manager in hot code path (Jukka Lehtosalo, PR 14331)
Change various type queries into faster bool type queries (Jukka Lehtosalo, PR 14330)
Speed up recursive type check (Jukka Lehtosalo, PR 14326)
Optimize subtype checking by avoiding a nested function (Jukka Lehtosalo, PR 14325)
Optimize type parameter checks in subtype checking (Jukka Lehtosalo, PR 14324)
Speed up freshening type variables (Jukka Lehtosalo, PR 14323)
Optimize implementation of TypedDict types for **kwds (Jukka Lehtosalo, PR 14316)
Warn About Variables Used Before Definition
Mypy will now generate an error if you use a variable before it’s defined. This feature is enabled by default. By default mypy reports an error when it infers that a variable is always undefined.
y = x # E: Name "x" is used before definition [used-before-def]
x = 0
A new experimental possibly-undefined error code is now available that will detect variables that may be undefined:
if b:
x = 0
print(x) # Error: Name "x" may be undefined [possibly-undefined]
The error code is disabled be default, since it can generate false positives.
This feature was contributed by Stas Ilinskiy.
Support the “Self” Type
There is now a simpler syntax for declaring generic self types introduced in PEP 673: the Self type. You no longer have to define a type variable to use “self types”, and you can use them with attributes. Example from mypy documentation:
from typing import Self
class Friend:
other: Self | None = None
@classmethod
def make_pair(cls) -> tuple[Self, Self]:
a, b = cls(), cls()
a.other = b
b.other = a
return a, b
class SuperFriend(Friend):
pass
# a and b have the inferred type "SuperFriend", not "Friend"
a, b = SuperFriend.make_pair()
The feature was introduced in Python 3.11. In earlier Python versions a backport of Self is available in typing_extensions.
This was contributed by Ivan Levkivskyi (PR 14041).
Support ParamSpec in Type Aliases
ParamSpec and Concatenate can now be used in type aliases. Example:
from typing import ParamSpec, Callable
P = ParamSpec("P")
A = Callable[P, None]
def f(c: A[int, str]) -> None:
c(1, "x")
This feature was contributed by Ivan Levkivskyi (PR 14159).
ParamSpec and Generic Self Types No Longer Experimental
Support for ParamSpec (PEP 612) and generic self types are no longer considered experimental.
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:
Alessio Izzo
Alex Waygood
Anders Kaseorg
Andrzej Bartosiński
Avasam
ChristianWitzler
Christoph Tyralla
dosisod
Harrison McCarty
Hugo van Kemenade
Hugues
Ilya Konstantinov
Ivan Levkivskyi
Jelle Zijlstra
jhance
johnthagen
Jonathan Daniel
Joshua Bronson
Jukka Lehtosalo
KotlinIsland
Lakshay Bisht
Lefteris Karapetsas
Marc Mueller
Matthew Hughes
Michael Lee
Nick Drozd
Nikita Sobolev
Richard Si
Shantanu
Stas Ilinskiy
Tim Geypens
Tin Tvrtković
Tom Schraitle
Valentin Stanciu
Vincent Vanlaer
We’d also like to thank our employer, Dropbox, for funding the mypy core team.
