Collection of Hashable doesn't work properly

[SLAPaper]

# test_hashable.py
from typing import List, Set, Hashable

test_int: int = 5
test_hashable: Hashable = test_int

test_list1 = [1, 2, 3]
test_list2: List[Hashable] = test_list1

test_set1: Set[int] = {1, 2, 3}
test_set2: Set[Hashable] = test_set1

def f(key_set: Set[Hashable]) -> None:
    pass

f(test_set1)

> mypy .\test_hashable.py
test_hashable.py:7: error: Incompatible types in assignment (expression has type "List[int]", variable has type "List[Hashable]")
test_hashable.py:10: error: Incompatible types in assignment (expression has type "Set[int]", variable has type "Set[Hashable]")
test_hashable.py:15: error: Argument 1 to "f" has incompatible type "Set[int]"; expected "Set[Hashable]"

> mypy -V
mypy 0.701

> python -V
Python 3.7.3

int itself seems to be recognized as Hashable correctly since #1746, but collections of Hashable seems not accepting collections of int.
Is this behavior expected and I'm doing something wrong? If so, then what type annotaion should I write when I want a collection of dictionary keys?

[JelleZijlstra]

This is related to invariance; you can read up on this in the docs. Your code is unsafe because something like this could happen:

x: List[int] = [1, 2, 3]
y: List[Hashable] = x
y.append("string")

for element in x:
    print(element + 1)  # blows up because x now contains a string, even though it's a List[int]

You can fix type checking by using covariant container types like Sequence or Iterable instead.