Python typing

Type annotations in python.

Example

from typing import Dict, List, Tuple
from typing import Optional, Union

class Project:
    def ex_param_w_return(user: User) -> bool

    def ex_type_w_default(active: bool=False) -> None:

    def ex_no_return() -> None:

    def ex_generics(data: List[Dict]):

    def ex_optional() -> Optional[str]:  # nullable type

    def ex_type_or_other_type(id: Union[str, int]) -> None:

Common Types

functions/lambdas

from typing import Callable

def run_callback(cb: Callable[[str, int], bool]) -> None:

dates/times

import datetime

def foo() -> datetime.datetime:
    return datetime.datetime.now()

def foo() -> datetime.date:
    return datetime.date.today()

open file objects

from typing import IO

# either bytes/str
def foo() -> IO:
    return open('foo.txt', 'r')

def foo() -> IO[bytes]:
    return open('foo.txt', 'rb')

def foo() -> IO[str]:
    return open('foo.txt', 'r')

context managers

@contextlib.contextmanager
def foo() -> Iterator[str]:
    print('foo')
    yield 'bar'
    print('baz')

dataclasses (structs)

They're already typed. See python datatypes

import dataclasses

@dataclasses.dataclass
class User
    id: int
    name: str

Implementing Generics

TODO:

improve, w/ usage example

from typing import Generic, TypeVar

T = TypeVar('T')

class Range(Generic[T]):
    start: T
    end: T