Oops, look like I took this off-list by accident -- bringing it back on.

On Fri, Aug 28, 2020 at 12:50 PM Guido van Rossum <gu...@python.org> wrote:

> IMO the bar for attempting to solve this is pretty high, since I can think
> of no way to solve it without breaking old code that doesn't involve
> introducing new names.
>

Exactly -- so we're kind of stuck with the existing ABCs for a good long
while. Maybe that's OK, but it does mean we are choosing to freeze at least
this part of Python.

But I agree with you that it's problematic to add features to the builtins
as well (like .get() to list and friends that aren't in the ABCs, so we're
really freezing a lot of the language.

Which may be a good thing, but on this list at least, I expect people wont
like that :-)

FWIW I don't think there's an exception for dunders -- if we were to add
> Sequence.__new_dunder__ we'd still break code due to register().
>

hmm -- I never actually used register(), and had always assumed that it did
some checking -- but  apparently not, so yes, anything registered with an
ABC that something was added to could now be broken thanks for the tip.

Though that's probably less breakage, but breakage all the same.

-CHB


-- 
Christopher Barker, PhD

Python Language Consulting
  - Teaching
  - Scientific Software Development
  - Desktop GUI and Web Development
  - wxPython, numpy, scipy, Cython
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