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Python standard library: typing

Any

Any is the default annotation for all arguments or return types that are not explicitely specified.

Callable

Callable[ [t1, t2], tr ] is a callback function that expects two arguments of types t1 and t2 and returns a tr.

It's possible to define only the return type: Callable[ ..., tr]. (Note there are no square brackets around the ellipsis).

Dict

from typing import Dict

opts: Dict[int, str] = {}

def add_opt(k: int, v: str) -> None:
    opts[k] = v


def show_kv(d: Dict[int, str]):
    for k in d:
        print(str(k) + ': ' + d[k])


add_opt(4, 'four' )
add_opt(1, 'one'  )
add_opt(8, 'eight')

show_kv(opts)

Compare with Mapping.

Mapping

Compare with Dict and MutableMapping.

None

The return type of __init__ should be annotated with -> None.

NoReturn

NoReturn indicates that a a function does not return normally, such as sys.exit.

from typing import NoReturn

def fail() -> NoReturn:
    raise RuntimeError('failed')

Optional

from typing import Optional

def p(a: Optional[int] = 42, b: Optional[str] = 'Hello world'):
    print(f'a = {a}')
    print(f'b = {b}')

p(b='hi')

Sequence

Sequence[int]

TypeVar

from typing import TypeVar
x = TypeVar('y')

$ pyright /tmp/u.py
  /tmp/u.py:2:1 - error: TypeVar must be assigned to a variable named "y" (reportGeneralTypeIssues)

TYPE_CHECKING

Static type checkers must treat typeing.TYPE_CHECKING as True.

typing.TYPE_CHECKING will be deprecated.

See also PEP 781 (Make TYPE_CHECKING a built-in constant)