Hello everybody, I just publish the PEP-0604 <https://www.python.org/dev/peps/pep-0604/> for discussions (https://www.python.org/dev/peps/pep-0604/). Scala 3 propose a new syntax for Union type. See here <https://dotty.epfl.ch/docs/reference/new-types/union-types.html>. I propose to add a similar syntax in Python. # Operator for Union assert( int | str == Union[int,str]) assert( int | str | float == Union[int,str,float]) # Operator for Optional assert( ~int == Optional[int]) Now, it's possible to write: def fn(bag:List[int | str], option: ~int = None) -> float | str: ... in place of def fn(bag:List[Option[int,str]], option: Optional[int] = None) -> Union[float,str]: ... The discussion on python-new@python.org here <https://mail.python.org/archives/list/python-ideas@python.org/thread/FCTXGDT...> have emerged the idea of extending also issubclass() and isinstance(). isinstance(int, int | str) I think these syntaxes are more clear, and can help with the adoption of typing. I test and implement these ideas in a two fork : One for CPython <https://github.com/pprados/cpython/tree/updage_isinstance> and one for MyPy <https://github.com/pprados/mypy/tree/add_INVERT_to_types>. See the branches add_OR_to_types (for Union syntax), add_INVERT_to_types (for Union and Optional syntax) or updage_isinstance (for new isinstance() and issubclass()). How I implement that ? I add the operators __or__ and __revert__ to PyType_Type. The C code is similar of : from typing import * def type_or(self,right): return Union[self,right] type(type).__or__ = type_or with some check before return Union. Actually, the accepted BNF syntax for typing is : annotation: name_type name_type: NAME (args)? args: '[' paramslist ']' paramslist: annotation (',' annotation)* [','] I propose to extend the BNF syntax to : annotation: ( name_type | or_type | invert_type ) name_type: NAME (args)? args: '[' paramslist ']' paramslist: annotation (',' annotation)* [','] or_type: name_type '|' annotation invert_type: '~' annotation Your remarks are welcome. Philippe Prados