[Python-Dev] Re: lists v. tuples

[Guido van Rossum]

> > > Sorting plays with mutability by working in-place, but for many
> > > uses it would be just as good if sorting returned a sorted copy
> > > instead -- the key thing here is the sorting, not the mutability.
> >
> > And the key assumption for sorting things is that
> > the things are sortable, which means there
> > exists and order on the basic set.
> > Which again suggests that list elements usually
> > have something in common.
> 
> If a list contains ONE complex number and no other number,
> then the list can be sorted.

But the order isn't meaningful.

> If the list contains elements that having something in common,
> by both being complex numbers, then it cannot be sorted.
> 
> So, lists whose elements have LESS in common (by being of
> widely different types) are more likely to be sortable than lists
> some of whose elements have in common the fact of being
> numbers (if one or more of those numbers are complex).
> 
> Although not likely to give practical problems (after all I suspect
> most Pythonistas never use complex numbers at all), this
> anomaly (introduced in 1.6, I think) makes conceptualization
> less uniform and thus somewhat harder to teach.

If I had to do it over again, I'd only implement == and != for objects
of vastly differing types, and limit <, <=, >, >= to objects that are
meaningfully comparable.

I'd like to to this in Python 3.0, but that probably means we'd have
to start deprecating default comparisons except (in)equality in Python
2.4.

--Guido van Rossum (home page: http://www.python.org/~guido/)