#9362: Invalidate None as a vertex label.
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Reporter: boothby | Owner: jason, mvngu, ncohen, rlm
Type: defect | Status: new
Priority: major | Milestone:
Component: graph theory | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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The following indicates to me a huge problem:
{{{
sage: G = Graph()
sage: G.add_edge(None, 1)
sage: G.show()
}}}
the resulting plot has three vertices, one blank, one labeled "1" and the
other labeled "None". The blank vertex is floating off in space, and the
None and 1 vertices are bunched together.
This indicates to me that we should not accept "None" as a valid vertex
label.
Other places where a vertex labeled None will obviously cause problems:
{{{spanning_trees_count}}}, {{{add_vertex}}}, {{{add_edge}}},
{{{delete_edge}}}, {{{has_edge}}}, {{{edge_label}}}, {{{eccentricity}}},
{{{layout_tree}}}
this is not an exhaustive list; I merely read method definitions to look
where a vertex argument defaults to None (and later uses the condition
{{{if v is None}}}).
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9362>
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