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PYDANTIC FIXES TYPE VARIABLE BUG IN SUBCLASS GENERICS
By RepoJournal ยท Filed ยท About FastAPI & Pydantic ยท Composed from the cited sources ยท methodology
2 people shipped this
Pydantic shipped a fix for type variable substitution failures in `__pydantic_extra__` when subclassing generic models, closing a long-standing issue that broke runtime validation for inherited types.
The fix [1] targets a core validation gap where type variables weren't properly substituted in extra attributes during subclass inheritance, a scenario that breaks serialization and validation pipelines relying on generic base classes. This is the kind of subtle bug that manifests in production when you're using discriminated unions or parameterized base models across a deep inheritance chain. FastAPI developers working with complex domain models should test their generic inheritance patterns after this lands [2]. On the sponsorship front, FastAPI's people roster got updated [3], reflecting the project's growing ecosystem of supporters. Nothing breaking in either shop; this is pure stability work.
Action items
- โ Test generic model inheritance and __pydantic_extra__ access in your codebase pydantic/pydantic [plan]
- โ Watch for Pydantic's next release to pull in the type variable fix pydantic/pydantic [monitor]
References
- [1] Fix type variable substitution in `__pydantic_extra__` with subclasses โ pydantic/pydantic
- [2] Fix type variable substitution in `__pydantic_extra__` with subclasses (#13483) โ pydantic/pydantic
- [3] ๐ฅ Update FastAPI People - Sponsors โ fastapi/fastapi
