[Python-Dev] Type hints -- a mediocre programmer's reaction

[Cory Benfield]

On 21 April 2015 at 17:59, Guido van Rossum <guido at python.org> wrote:
> For me, PEP 484 is a stepping stone. Among the authors of PEP 484 there was
> much discussion about duck typing, and mypy even has some limited support
> for duck typing (I think you can still find it by searching the mypy code
> for "protocol"). But we ran out of time getting all the details written up
> and agreed upon, so we decided to punt -- for now. But duck typing still
> needs to have a way to talk about things like "seek method with this type
> signature" (something like `def seek(self, offset: int, whence:
> int=SEEK_SET) -> int`) so the current proposal gets us part of the way
> there.
>
> The hope is that once 3.5 is out (with PEP 484's typing.py included
> *provisional* mode) we can start working on the duck typing specification.
> The alternative would have been to wait until 3.6, but we didn't think that
> there would be much of an advantage to postponing the more basic type
> hinting syntax (it would be like refusing to include "import" until you've
> sorted out packages). During the run of 3.5 we'll hopefully get feedback on
> where duck typing is most needed and how to specify it -- valuable input
> that would be much harder to obtain of *no* part of the type hints notation
> were standardized.

This makes a lot of sense.

If PEP 484 is intended to be a stepping stone (or compromise, or beta,
or whatever word one wants to use), then it is easy to forgive it its
limitations, and I'm looking forward to seeing it improve.