type-name-incorrect-variance (PLC0105)
Added in v0.0.278 · Related issues · View source
Derived from the Pylint linter.
What it does
Checks for type names that do not match the variance of their associated type parameter.
Why is this bad?
PEP 484 recommends the use of the _co and _contra suffixes for
covariant and contravariant type parameters, respectively (while invariant
type parameters should not have any such suffix).
Example
from typing import TypeVar
T = TypeVar("T", covariant=True)
U = TypeVar("U", contravariant=True)
V_co = TypeVar("V_co")
Use instead:
from typing import TypeVar
T_co = TypeVar("T_co", covariant=True)
U_contra = TypeVar("U_contra", contravariant=True)
V = TypeVar("V")