add return type in python 3 code example

Example 1: specify return type python function

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

Example 2: python type hint list

# For collections, the name of the type is capitalized, and the
# name of the type inside the collection is in brackets
x: List[int] = [1]
x: Set[int] = {6, 7}
  
# For simple built-in types, just use the name of the type
x: int = 1
x: float = 1.0
x: bool = True
x: str = "test"
x: bytes = b"test"