BSK-E0026 error

TypeVar declared with exactly one constraint

PEP 484 requires a TypeVar to have either zero constraints (unconstrained) or two or more constraints. A single constraint makes no sense because it would be equivalent to using the type directly.

Real basilisk check output

What you see when BSK-E0026 fires on a minimal example:

basilisk check output reporting BSK-E0026 — `TypeVar` declared with exactly one constraint

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial BSK-E0026 down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type Safety rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/BSK-E0026