[Python-3000] PEP 3119 "Open issues"

[James Thiele]

PEP 3119 has some "Open issues", three of which I list below. These
have (I assume) probably been resolved but it is hard to know what
search terms to use to find them in this mailing list. It would be
useful to record the decisions in the PEP, or at least resolve them if
they are still open issues.

(in "One Trick Ponies") Open issues: Conceivably, instead of using the
ABCMeta metaclass, these classes could override __instancecheck__ and
__subclasscheck__ to check for the presence of the applicable special
method

(in Sequence) Open issues: Other candidate methods, which can all have
default concrete implementations that only depend on __len__ and
__getitem__ with an integer argument: __reversed__, index, count,
__add__, __mul__.

(in Strings) Open issues: define the base interfaces for these so
alternative implementations and subclasses know what they are in for.
This may be the subject of a new PEP or PEPs (PEP 358 should be
co-opted for the bytes type).