On Sat, 4 Jul 2020 at 12:51, Random832 <random...@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.
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