#17086: GenericGraph's documentation, __eq__, and __hash__ out of sync
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Reporter: emassop | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: graph theory | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/emassop/graph_hash | 82b245ee0b092a7a994074e27cc47686d43551c9
Dependencies: | Stopgaps:
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Comment (by ncohen):
Hello !
Thank you for this 'Counter' thing, I did not know that it existed `^^;`
1) About `self.edge_iterator(labels = self._weighted)`:
You can have graphs with edge labels for which _weighted is not True
{{{
sage: Graph([(1,2,"Hey")])._weighted
False
sage: Graph([(1,2,"Hey")],immutable=True)._weighted
False
}}}
I do not think that this 'weighted' notion makes a lot of sense anyway,
perhaps we should remove it. Either way it is probably best to set
'labels' to `True` anytime.
2) Perhaps I do not understand what your tests do, but even when the graph
is immutable the list of vertices returned by `.vertices()` should be
sorted. Do you have a counterexample to that ?
Indeed, we cannot assume that sorting a list produces a unique sorted
list (because the order is not always a total order) but that list,
however, should be sorted.
This, because even when the immutable graph is created, the vertices are
labelled using the order returned by `.vertices()`. So I hope that you
found no bad behaviour there.
But indeed, wrapping it with a frozenset if the right thing to do.
3) Technically, you do not need to add `._is_weighted` in the hash
function, as graphs with different values for `._is_weighted` are nonequal
anyway. But that does not hurt either.
4) `O_O`
{{{
sage: G1 = Graph({0: {1: 'edge label A'}})
sage: G2 = Graph({0: {1: 'edge label B'}})
sage: G1 == G2
True
}}}
This is *REALLY* bad ! Graphs with different labels should be non-equal
!!! `O_O;;;;;`
But it seems that it has been like that forever... Gosh that's bad `O_o`
Hmmmm.. Now I understand why you added this `self._weighted` in the hash
function `:-/`
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/17086#comment:3>
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