python method return type code example

Example 1: python typing list of strings

from typing import List

def my_func(l: List[int]):
    pass

Example 2: specify return type python function

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

Example 3: typing generator python

# Iterator
def infinite_stream(start: int) -> Iterator[int]:
    while True:
        yield start
        start += 1

# Generator        
def infinite_stream(start: int) -> Generator[int, None, None]:
    while True:
        yield start
        start += 1

Example 4: 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