#14794: DiGraph constructor doc describes `boundary` option wrong
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Reporter: mguaypaq |
Owner: mguaypaq
Type: defect |
Status: new
Priority: major |
Milestone: sage-5.12
Component: PLEASE CHANGE |
Keywords: graph, digraph, mutable default
Work issues: fix digraph documentation, get rid of mutable defaults |
Report Upstream: N/A
Reviewers: |
Authors: Mathieu Guay-Paquet
Merged in: |
Dependencies:
Stopgaps: |
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While working on quivers `sage.quivers.*` we ran into some confusing
documentation in `DiGraph` about the `boundary` argument of the
constructor:
{{{
- ``boundary`` - a list of boundary vertices, if none,
digraph is considered as a 'digraph without boundary'
}}}
Here, it turns out that `None` is not actually allowed, and instead an
empty list `[]` should be used instead. This is described more clearly in
the `Graph` docstring:
{{{
- ``boundary`` - a list of boundary vertices, if
empty, graph is considered as a 'graph without boundary'
}}}
An example of a problem:
{{{
sage: DiGraph()
Digraph on 0 vertices
sage: show(DiGraph())
sage: show(DiGraph(boundary=[]))
sage: show(DiGraph(boundary=None))
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
...
TypeError: object of type 'NoneType' has no len()
}}}
As a separate point, both `Graph.__init__` and `DiGraph.__init__` have
mutable default arguments (`def __init__(..., boundary=[], ...)`) which is
frowned upon.
I'll put up a patch in a few minutes.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14794>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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