On Sun, Nov 29, 2020 at 1:49 AM Guido van Rossum <gu...@python.org> wrote:
> On Sat, Nov 28, 2020 at 9:32 AM Andrew Svetlov <andrew.svet...@gmail.com>
> wrote:
>
>> I would see support of all argument kinds support in any proposal for a
>> new callable: positional only args, named args, keyword-only, *args and
>> **kwargs.
>> The exact notation in probably less important than missing functionality.
>>
>
> Hm, but using Protocol you can already express every callable type. We
> could duplicate all of the complexity of 'def' parameter lists into the
> type notation, but it would be very complex. So this requirement is at
> least debatable (I'm not actually sure how I feel about it).
>
>
Don't get me wrong please. I'm not the typing system developer (while use
typing every day in my code).
You can consider this email as end-user feedback.
I have a lot of code that uses `Callable[]` annotation; it is a natural way
of annotating any callable, isn't it.
Sometimes `Callable` doesn't work. For example, I cannot annotate a
function that accepts a keyword-only argument.
Sure, I can use Protocol but it doesn't feel natural and requires more code
lines, especially if the Protocol is used once or twice.
Also, Protocol adds `self` to methods which looks at least confusing when I
annotate plain callables which naturally don't belong to any class:
class MyFunc(typing.Protocol):
def __call__(self, /, arg: int) -> str: ...
Moreover, I recall a pull request to only of my libraries that had
something similar to:
class MyProto(typing.Protocol):
def __call__(self_, /, self: Class, arg: int) -> str: ...
The protocol actually had two 'self': one fake self for protocol itself and
another one if the *real* self.
The PR was refactored to use a more *natural* style but my first reaction
was eyeballs :)
The last thing that is unclear for me is mixing protocols with ParamSpec
from PEP-612.
Sure, I can live with all the mentioned limitations and learn all the
required tricks if we have a consensus that Callable should operate with
positional unnamed arguments only; but allowing to write such things in a
manner similar to that Python supports for function definitions already
makes life easier.
--
Thanks,
Andrew Svetlov
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