invalid-index-type (RUF016)

What it does

Checks for indexed access to lists, strings, tuples, bytes, and comprehensions using a type other than an integer or slice.

Why is this bad?

Only integers or slices can be used as indices to these types. Using other types will result in a TypeError at runtime and a SyntaxWarning at import time.

Example

var = [1, 2, 3]["x"]

Use instead:

var = [1, 2, 3][0]