On 9/27/2017 5:28 AM, Ivan Levkivskyi wrote:
Abstract
========
Initially PEP 484 was designed in such way that it would not introduce
*any* changes to the core CPython interpreter. Now type hints and
the ``typing`` module are extensively used by the community, e.g. PEP 526
and PEP 557 extend the usage of type hints, and the backport of ``typing``
on PyPI has 1M downloads/month. Therefore, this restriction can be removed.
It seem sensible to me that you waited awhile to discover what would be
needed.
It is proposed to add two special methods ``__class_getitem__`` and
``__subclass_base__`` to the core CPython for better support of
generic types.
I would not be concerned about anyone (mis)using reserved words.
If the new methods were for general use, I would question making them
automatically class methods. Having __new__ automatically being a
static method is convenient, but occasionally throws people off. But if
they were only used for typing, perhaps it is ok. On the other hand, I
expect that others will use __class_getitem__ for the same purpose -- to
avoid defining a metaclass just to make class[something] work. So I
question defining that as 'typing only'.
Without rereading the PEP, the use case for __subclass_base__ is not
clear to me. So I don't know if there are other uses for it.
--
Terry Jan Reedy
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