I don’t know if this has been discussed before.
Similar to PEP 645 idea of writing "Optional[type]" as “type?”, I propose we write "Callable[[type1, type2, ...], type3]” as “[type1, type2, … -> type3]”. Look at the two examples below and see which one looks better to the eyes:
def func1(f: typing.Callable[[str, int], str], arg1: str, arg2: int) -> str:
return f(arg1, arg2)
def func2(f: [str, int-> str], arg1: str, arg2: int) -> str:
return f(arg1, arg2)
There is less clutter especially if we have nested Callables.
e.g., f: Callable[[str, int], Callable[[int,…], str]] becomes f: [str, int -> [int, ... -> str]]
Callable without zero arguments.. f: Callable[[], str] would become f: [ -> str]
Equivalent to Callable alone without caring about arguments and the return value would be [… -> typing.Any] or [… -> ]
Let’s say we have a function that accepts a decorator as an argument. This might not be useful to do, but I want to show case how it would be easier to read. The old way would be:
def decorator(f: Callable[…, int]) -> Callable[…, tuple[int, str]]:
def wrapper(*args, **kwargs) -> tuple[int, str]:
text = “some text”
res = f(*args, **kwargs)
return res, text
return wrapper
def function(decorator: Callable[[Callable[…, int]], Callable[…, tuple[int, str]]], decorated_on: Callable[…, int]) -> Callable[…, tuple[int, str]]:
wrapper = decorator(decorated_on)
return wrapper
The new way is as follows:
def decorator(f: [… -> int]) -> [… -> tuple[int, str]]:
def wrapper(*args, **kwargs) -> tuple[int, str]:
text = “some text”
res = f(*args, **kwargs)
return rest, text
return wrapper
def function(decorator: [ [… -> int] -> [… -> tuple[int, str]]], decorated_on: [… -> int]) -> [… -> tuple[int, str]]:
wrapper = decorator(decorated_on)
return wrapper
I saw something similar in Pylance type checker (VSC extension) when you hover over an annotated function that has Callable as an argument or a return value, but they don’t seem to use brackets to mark the beginning and end of the callable, which could be hard to follow mentally (see screenshot below)
<Screen Shot 2020-11-28 at 8.30.09 PM.png>
Personally, I think it would be easier if Pylance wrote the hint like the following:
(function) function: (decorator: [p0:[*args: Any, **kwargs: Any -> int ]] -> [*args: Any, **kwargs: Any -> tuple[int, str]], decorated_on: [*args: Any, **kwargs: Any -> int]) -> [*args: Any, **kwargs: Any -> tuple[int, str]]