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)
Fixes to Cache Corruption
- Fix generic TypedDict/NamedTuple caching (Ivan Levkivskyi, PR 14675)
Mypyc Fixes and Improvements
- Raise "non-trait base must be first..." error less frequently (Richard Si, PR 14468)
- Generate faster code for bool comparisons and arithmetic (Jukka Lehtosalo, PR 14489)
- Optimize __(a)enter__/__(a)exit__ for native classes (Jared Hance, PR 14530)
- Detect if attribute definition conflicts with base class/trait (Jukka Lehtosalo, PR 14535)
- Support __(r)divmod__ dunders (Richard Si, PR 14613)
- Support __pow__, __rpow__, and __ipow__ dunders (Richard Si, PR 14616)
- Fix crash on star unpacking to underscore (Ivan Levkivskyi, PR 14624)
- Fix iterating over a union of dicts (Richard Si, PR 14713)
Fixes to Detecting Undefined Names (used-before-def)
- Correctly handle walrus operator (Stas Ilinskiy, PR 14646)
- Handle walrus declaration in match subject correctly (Stas Ilinskiy, PR 14665)
Stubgen Improvements
Stubgen is a tool for automatically generating draft stubs for libraries.
- Allow aliases below the top level (Chad Dombrova, PR 14388)
- Fix crash with PEP 604 union in type variable bound (Shantanu, PR 14557)
- Preserve PEP 604 unions in generated .pyi files (hamdanal, PR 14601)
Stubtest Improvements
Stubtest is a tool for testing that stubs conform to the implementations.
- Update message format so that it’s easier to go to error location (Avasam, PR 14437)
- Handle name-mangling edge cases better (Alex Waygood, PR 14596)
Changes to Error Reporting and Messages
- Add new TypedDict error code typeddict-unknown-key (JoaquimEsteves, PR 14225)
- Give arguments a more reasonable location in error messages (Max Murin, PR 14562)
- In error messages, quote just the module's name (Ilya Konstantinov, PR 14567)
- Improve misleading message about Enum() (Rodrigo Silva, PR 14590)
- Suggest importing from typing_extensions if definition is not in typing (Shantanu, PR 14591)
- Consistently use type-abstract error code (Ivan Levkivskyi, PR 14619)
- Consistently use literal-required error code for TypedDicts (Ivan Levkivskyi, PR 14621)
- Adjust inconsistent dataclasses plugin error messages (Wesley Collin Wright, PR 14637)
- Consolidate literal bool argument error messages (Wesley Collin Wright, PR 14693)
Other Fixes and Improvements
- 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.
