narrowing_typeis_2 error

TypeIs narrows to a type inconsistent with the input type

Per the typing spec: "It is an error to narrow to a type that is not consistent with the input type." For TypeIs, the narrowed type must be a subtype of the input type.

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial narrowing_typeis_2 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/narrowing_typeis_2