How to avoid mypy complaints when inheriting from a built-in collection type?

Question

Running mypy on code like this

class MySpecialList(list):
   # funky extra functionality

gives me

my_file.py:42: error: Missing type parameters for generic type "list"  [type-arg]

I can avoid this by not inheriting from list at all or ignoring this error.

But how should I deal with this? Isn't this a bug in mypy?

Answer 1

This is the result of using --disallow-any-generics (which is implied by --strict), as list is equivalent to list[Any]. You can fix it by making MySpecialist explicitly generic via a type variable.

from typing import TypeVar


T = TypeVar('T')


class MySpecialList(list[T]):
    ...