from typing import reveal_type

def f(x: int | bool):  # does not narrow
  if type(x) is bool:
    x = 42
  reveal_type(x)


def g(x: int | None):  # works OK
  if x is None:
    x = 42
  reveal_type(x)

 INFO revealed type: bool | int [reveal-type]
 --> /tmp/foo.py:6:14
  |
6 |   reveal_type(x)
  |              ---
  |
 INFO revealed type: int [reveal-type]
  --> /tmp/foo.py:12:14
   |
12 |   reveal_type(x)
   |              ---
   |
 INFO 0 errors