Union alias (PEP-604)

PEP-604 (landed in Python 3.10) introduced a new short syntax for typing.Union (as I predicted, but I messed up union with intersection, shame on me):

def greet(name: str) -> str | None:
  if not name:
    return None
  return f"Hello, {name}"

You already can use it in older Python versions by adding from __future__ import annotations, type checkers will understand you.