So it is a verb. ;-)
Looks like similar comments apply to edges().
I'm thinking that optionally passing in a comparison function would be
a nice thing to add - a minor convenience, but also it would drive
home the point that the sorting is somewhat the caller's
responsibility in non-trivial situations (ie for not most users).
I'll get a ticket started soon.
Rob
On Jul 24, 4:27 am, Robert Miller <r...@rlmiller.org> wrote:
> I would simply add a caveat to the documentation. Most users use
> either integers for vertices, or a set of certain kinds of objects. It
> should be noted that "<" should implement a total ordering for this to
> be consistent, e.g. not just a poset. This is related to a debate
> about whether "<" should give an ordering of poset elements for
> computer science reasons (like binary search in a list) or for
> mathematicians...
>
>
>
> On Sat, Jul 24, 2010 at 9:20 AM, Rob Beezer <goo...@beezer.cotse.net> wrote:
> > The vertices() method for graphs says the resulting list is always
> > sorted. But while you can use a variety of objects as the vertices of
> > a graph (very nice), they do not always compare cleanly (not so
> > nice). So I got bit tonight on a doctest where one vertex was an
> > integer and one was a symbolic expression. With a randomized order
> > for the tests, the results would vary.
>
> > Do we need to be more careful about the vertices() method, either in
> > action or in claims? When the documentation says the list is sorted,
> > is "sorted" a verb or an adjective?
>
> > I presume it is expecting too much that any two objects can be
> > comparable somehow?
>
> > Rob
>
> > sage: var('x')
> > x
> > sage: G=Graph({0:[x]})
> > sage: vert = G.vertices()
> > sage: vert
> > [0, x]
> > sage: sorted(vert)
> > [0, x]
> > sage: vert.reverse()
> > sage: vert
> > [x, 0]
> > sage: sorted(vert)
> > [x, 0]
> > sage: G.vertices?
> > <snip>
> > Note that the output of the vertices() function is always sorted.
> > <snip>
>
> > --
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>
> --
> Robert L. Millerhttp://www.rlmiller.org/
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