Unsupported Dynamic Base

What it does

Checks for dynamic class definitions (using type()) that have bases which are unsupported by ty.

This is equivalent to unsupported-base but applies to classes created via type() rather than class statements.

Why is this bad?

If a dynamically created class has a base that is an unsupported type such as type[T], ty will not be able to resolve the method resolution order (MRO) for the class. This may lead to an inferior understanding of your codebase and unpredictable type-checking behavior.

Default level

This rule is disabled by default because it will not cause a runtime error, and may be noisy on codebases that use type() in highly dynamic ways.

Examples

class Base: ...


def factory(base: type[Base]) -> type:
    # `base` has type `type[Base]`, not `type[Base]` itself
    return type("Dynamic", (base,), {})  # error: [unsupported-dynamic-base]