You can do that in Python as well though.

  from typing import Union
   
  class Dog:
      dogtag: str
      name: str
  
  class Cat:
      name: str
      allowedOutside: bool
  
  Animal = Union[Cat, Dog]
  
  def do(a: Animal):
      print(a.name)  # Always allowed
      print(a.dogtag)  # MYPY error
      if isinstance(a, Dog):
          print(a.dogtag) # MYPY allows