Type hint a subclass of list

Question

I use a class which subclasses the built-in list.

class Qry(list):
    """Stores a list indexable by attributes."""

    def filter(self, **kwargs):
        """Returns the items in Qry that has matching attributes.

        Example:
            obj.filter(portfolio='123', account='ABC').
        """

        values = tuple(kwargs.values())

        def is_match(item):
            if tuple(getattr(item, y) for y in kwargs.keys()) == values:
                return True
            else:
                return False

        result = Qry([x for x in self if is_match(x)], keys=self._keys)

        return result

Now I want to type hint:

class C:
    a = 1

def foo(qry: Qry[C]):
    """Do stuff here."""

How do you type hint a custom container class in python 3.5+?

Answer 1

You can do this rather easily:

from typing import TypeVar, List
T = TypeVar('T')
class MyList(List[T]): # note the upper case
    pass