On Sun, May 28, 2017 at 8:27 AM, Ivan Levkivskyi <levkivskyi@gmail.com> wrote:

Regarding the title, I'd like to keep the word Protocol in the title too, so I'd go with "Protocols: Structural subtyping (duck typing)" -- hope that's not too long to fit in a PEP title field.

> Type-hints should not have runtime semantics, beyond those that they have as classes

>  lots of code uses isinstance(obj, collections.abc.Iterable) and similar checks with other ABCs

Having interfaces defined as something extended from abc doesn't necessitate their use at runtime, but it does open up a great deal of options for those of us who want to do so. I've been leveraging abc for a few years now to implement a lightweight version of what this PEP is attempting to achieve

IIUC this is not the main goal of the PEP, the main goal is to provide support/standard for _static_ structural subtyping.

Possibility to use protocols in runtime context is rather a minor bonus that exists mostly to provide a seamless transition

for projects that already use ABCs.

Is something like this already in the PEP? It deserves attention in one of the earlier sections.