On Sat, 4 Jul 2020 at 12:51, Random832 <random832@fastmail.com> wrote:
On Fri, Jul 3, 2020, at 03:57, Wes Turner wrote:
> Can a Sequence be infinite? If so, an equality test of two
> nonterminating sequences would be a nonterminating operation.

I think not - an infinite sequence would make len, contains, and reversed ill-defined (it also wouldn't allow certain kinds of slices)

> Do Sized and *Reversible* imply that a sequence terminates?
> Could __len__ return inf?

__len__ must return an integer.

> Perhaps `Ordered` is a requisite condition for defining a comparator
> for Sequences.
> `OrderedSequence`?
>
> Are there unordered Sequences for which a default `__eq__` / `__cmp__`
> (et. al) would be wrong or inappropriate?

I don't think so [index as a mixin implies being ordered, i think]... the bigger problem is the one I mentioned earlier, that allowing comparison between sequences of different types is inconsistent with tuple and list.

As far as types are concerned, the `__eq__` should worry about it - just Sequences that are
a subtype of other, or the other being a subtype of one, should be able to compare equal 
(As  happens with lists and tuples as well: subclasses of both will compare equal to base lists and tuples
with the same content.). 

The code for that is on my first reply to Guido, above:
       if not issubclass(type(other), type(self)) and not issubclass(type(self), type(other)):
            return False

I am actually using that on the file that motivated me sending the first e-mail here -as it
makes sense in that project.