return types in python code example

Example 1: specify return type python function

def greeting(name: str) -> str:
  return 'Hello, {}'.format(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