Graph([(0,'a')]).vertices() raises exception

[Georgi Guninski]

hi sage developers :)
long time no see.

i think the migration python2 to python3 regressed a lot
of Graph() stuff related to ordering the vertices.

Here is test case from sagecell:

===
g1=Graph([(0,'a')])
g2=g1.copy()
g2.relabel()
g2.vertices()
g1.vertices()

TypeError: '<' not supported between instances of 'int' and 'str'
===

[Dima Pasechnik]

On Wed, 13 Jul 2022, 08:17 Georgi Guninski, <ggun...@gmail.com> wrote:

hi sage developers :)
long time no see.

i think the migration python2 to python3 regressed a lot
of Graph() stuff related to ordering the vertices.

yes, indeed. I don't think much can be done here; i.e., fix your old code.

Here is test case from sagecell:

===
g1=Graph([(0,'a')])
g2=g1.copy()
g2.relabel()
g2.vertices()
g1.vertices()

TypeError: '<' not supported between instances of 'int' and 'str'
===

--
You received this message because you are subscribed to the Google Groups "sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/CAGUWgD-KgJS9CnNCJPun0TcQjbi6Y2RBS8JLYpca%3D1oPjLpi4w%40mail.gmail.com.

[John H Palmieri]

"Fix your old code" could just mean using `vertices(sort=False)`. See also https://trac.sagemath.org/ticket/22349.

[Georgi Guninski]

On Wed, Jul 13, 2022 at 5:46 PM John H Palmieri <jhpalm...@gmail.com> wrote:
>
> "Fix your old code" could just mean using `vertices(sort=False)`. See also https://trac.sagemath.org/ticket/22349.
>

fixing the sort() appears easy:

>>> li=['a',0]
>>> li.sort(key=hash);li
[0, 'a']

[John H Palmieri]

I see the following in the most recent (beta) release of Sage:

sage: g1=Graph([(0,'a')])
sage: g1.vertices()
<ipython-input-2-8314ec1f36bb>:1: DeprecationWarning: parameter 'sort' will be set to False by default in the future
See http://trac.sagemath.org/22349 for details.
  g1.vertices()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [2], in <cell line: 1>()
----> 1 g1.vertices()

File ~/Desktop/Sage/git/sage/src/sage/graphs/generic_graph.py:11196, in GenericGraph.vertices(self, sort, key, degree, vertex_property)
  11193     raise ValueError('sort keyword is False, yet a key function is given')
  11195 if sort:
> 11196     return sorted(self.vertex_iterator(degree=degree, vertex_property=vertex_property), key=key)
  11197 return list(self.vertex_iterator(degree=degree, vertex_property=vertex_property))

TypeError: '<' not supported between instances of 'int' and 'str'

You could instead use `g1.vertices(sort=False)` or as you suggested,  `g1.vertices(key=hash)`, but `g1.vertices()` with no extra arguments is going to produce an error.

[Travis Scrimshaw]

I think it is a very bad idea to have default sorting based upon hashing. This could make a lot of output appear seemingly random (despite having a natural order), nor there is no way to deal consistently with hash collisions. This would cause far more problems than it would solve when working with incomparable objects.

Best,

Travis