Python

Python does not implement type checking, use mypy to implement check

run it as part of your unit tests

#!/usr/bin/python

from typing import List

# declare variable type
# variable : type
numbers: List[int] = list(range(4))

# numbers2: List[str] = list(range(4)) # error by mypy

print(numbers)

# decleare function input and output types
# def function_name(parameter1: type) -> return_type:
def get_info(m: str) -> str:
    return 'Info: ' + m

def get_info2(m: int) -> str:
    return 'Info: ' + str(m)

print(get_info2('Hello')) # error by mypy

@overload-decorated definitions are for the benefit of the type checker only, they are not called at runtime

non-@overload-decorated definition will be called at runtime

#!/usr/bin/python

import typing

@typing.overload
def get_info(m: str) -> str:
    print('Call str type ...')
    return 'Info: ' + str(m)

@typing.overload
def get_info(m: int) -> str:
    print('Call int type ...')
    return 'Info: ' + str(m)

def get_info(m):
    print('Call general function ...')
    return 'Info: ' + str(m)

# general function will be call at run time
print(get_info(100))
print(get_info('Hello'))
print(get_info(3.14)) # error by type checker

Use Union to define either type contained in Union[]

#!/usr/bin/python

import typing

def get_info(m : typing.Union[int, str]) -> str:
    print('Call general function ...')
    return 'Info: ' + str(m)

print(get_info(100))
print(get_info('Hello'))
print(get_info(3.14)) # error by type checker

#!/usr/bin/python

from typing import List, Tuple, Dict, Set

l: List[int] = list(range(4))
t: Tuple[int, int] = (1, 2)
d: Dict[str, int] = {'Age': 38}
s: Set[int] = set([3, 2, 5, 6])

l_d: List[Dict[str, int]] = [{'Age': 39}, {'ID': 1}]

Take any data type

#!/usr/bin/python

import typing

def get_info(m : typing.Any) -> str:
    return 'Info: ' + str(m)

print(get_info(100))
print(get_info('Hello'))
print(get_info(3.14))

#!/usr/bin/python

import typing

def get_info(m : typing.Any) -> None:
    print('Info: ' + str(m))
    return 'Done' # error by type checker

get_info(100)

#!/usr/bin/python

import typing

Lint = typing.List[int]

def get_info(m : Lint) -> None:
    print('Info: ' + str(m))

get_info([1, 2, 3, 4])
get_info(100) # error by type checker

#!/usr/bin/python

import typing

T = typing.TypeVar('T', str, int)

def get_info(m : T, n : T) -> str:
    return str(m) + str(n)

print(get_info('Hello', 'World!'))
print(get_info(1, 2))
print(get_info(1, 'Hello')) # error by type checker
print(get_info(1, 3.14)) # error by type checker