generics_base_class_3 error

Invariant generic type mismatch at call site

When a function parameter expects a parameterised generic like dictstr, list[object] and a subclass whose base parameterisation differs in an invariant position is passed, the call is invalid.

class SymbolTable(dict[str, list[Node]]): ...

def takes(x: dict[str, list[object]]): ...

def test(s: SymbolTable):
    takes(s)  # E -- list is invariant, list[Node] != list[object]

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial generics_base_class_3 down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type System rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/generics_base_class_3