type hints python code example

Example 1: python type hints

def no_type_hint(arg):
  print(arg) # arg can be anything
  
def with_type_hint(arg: str):
  print(arg) # arg must be a string or a subtype of string

Example 2: python typing list of strings

from typing import List

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

Example 3: specify return type python function

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

Example 4: 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 5: 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"

Example 6: 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