Examples of Callable

Callable_examples.md

Some existing Callable types from github

Using the most restrictive full-stub syntax, here's how we'd express a few Callable types:

# from functools.pyi
f0: Callable[[_T1, _T2], S)
f0: (t1: _T1, t2: _T2, /) -> S

# from shapeflow/api.py
f1: Callable[[Optional[int], np.ndarray], stream_image]
f1: (i: Optional[int], a: np.ndarray, /) -> stream_image

# from pyexpat/__init__.pyi
f2: Callable[[str, Optional[str], int], Any]
f2: (s0: str, s1: Optional[str], i: int, /) -> Any

Here are the same examples if we allow underscores for irrelevant names:

f0: (_: _T1, _: _T2, /) -> S
f1: (_: Optional[int], _: np.ndarray, /) -> stream_image
f2: (_: str, _: Optional[str], _: int, /) -> Any

We also discussed making an underscore name always imply a positional-only argument, in which case we could omit the / and write:

f0: (_: _T1, _: _T2) -> S
f1: (_: Optional[int], _: np.ndarray) -> stream_image
f2: (_: str, _: Optional[str], _: int) -> Any

Here are the same examples if we allow a compact syntax for positional-only callable types:

f: (_T1, _T2) -> S
f1: (Optional[int], np.ndarray) -> stream_image
f2: (str, Optional[str], int) -> Any

A simple example type, with a few consistent stubs

Here's a callable type that can't be written using the existing Callable, expressed using each convention

# most restrictive stub syntax
(a: A, b: B = ..., /, c: C = ...) -> D

# stub syntax with _
(_: A, _: B = ..., /, c: C = ...) -> D


# if we let _ imply positional-only
(_: A, _: B = ..., c: C = ...) -> D

# if we allow no argument name for positional-only
(A, B = ..., c: C = ...) -> D

Here are several different function stubs that should typecheck when used as the type above:

def f0(a: A, b: B = ..., /, c: C = ...) -> D:
    ...

def f1(apple: A, bannana: SupertypeOfB = ..., c: C = ...) -> D:
    ...

def f2(apple: A, bannana: B = ..., *args: Any, **kwargs: Any) -> SubtypeOfD:
    ...