Hi,

Why not make Callable usable as a function decorator?



The motivating example in the PEP is this:


def flat_map(
     l: list[int],
     func: Callable[[int], list[int]]
) -> list[int]:
     ....


Since, as the PEP claims, `Callable[[int], list[int]]` is hard to read, then give it a name and use regular function definition syntax.


@Callable
def IntToIntFunc(a:int)->int:
     pass


def flat_map(
     l: list[int],
     func: IntToIntFunc
) -> list[int]:
     ....


To me, this seems much clearer than the proposed syntax and is more general.


It is a little longer, but unless you are playing code golf, that shouldn't matter.

Cheers,
Mark.



On 16/12/2021 5:57 pm, Steven Troxler wrote:
> Hello all,
>
> Thanks everyone for comments on our earlier thread [1] about callable type syntax. We now  have a draft PEP [2] proposing an arrow-based syntax for callable types, for example:
>
> ```
> (int, str) -> bool     # equivalent to Callable[[int, str], bool]
> ```
>
> In support of the PEP we also have:
> - a reference implementation of the parser [3] to ensure the grammar is correct  (tests [5], [6], [7])
> - a detailed specification of planned runtime behavior [4], which is not yet in the reference implementation
>
> We'd like to get your feedback about the PEP in general, and especially details and edge cases we need to consider regarding runtime behavior.
>
> Cheers,
> Steven Troxler
>
> ---------
> [1] Earlier python-dev thread https://mail.python.org/archives/list/python-dev@python.org/thread/VBHJOS3LOXGVU6I4FABM6DKHH65GGCUB/
> [2] PEP 677: https://www.python.org/dev/peps/pep-0677/
> [3] Reference implementation of Parser: https://github.com/stroxler/cpython/tree/callable-type-syntax--shorthand
> [4] Details on the runtime behavior:  https://docs.google.com/document/d/15nmTDA_39Lo-EULQQwdwYx_Q1IYX4dD5WPnHbFG71Lk/edit
>
> [5] Ast tests for parser changes:
> https://github.com/stroxler/cpython/blob/20eb59fdca0d6d8dbe4efa3b04038c7c22024654/Lib/test/test_ast.py#L359-L392
> [6] Easy-read tests of examples from the PEP: https://github.com/stroxler/cpython/blob/callable-type-syntax--shorthand/Lib/test/test_callable_type_examples_for_pep.py
> [7] Test sanity checking hundreds of examples pulled from typeshed:
> https://github.com/stroxler/cpython/blob/callable-type-syntax--shorthand/Lib/test/test_callable_type_examples_for_pep.py
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