python union on string type annotation code example

Example 1: type declaration python

def greeting(name: str) -> str:
    return 'Hello ' + name

Example 2: python optional type annotation

from custom_module import SomeClass
from typing import Optional

class SubClass:
    a_reference: Optional[SomeClass] # Provides info that a_reference may be 'None'.

    def __init__(self):
        self.a_reference = None