Hello everybody !!!
I am working with operators these days, and I wondered if there was a
reason behind the fact that defining the + operator does not mean the
"sum" function will work.
For graphs, the + operator means the disjoints union. Why shouldn't
the following code be accepted by Sage ?
sage: g = graphs.PetersenGraph()
sage: h = graphs.PetersenGraph()
sage: sum([g,h])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
/home/marsu/.sagebin/devel/sage-main/sage/graphs/<ipython console> in <module>()
/home/marsu/.sagebin/local/lib/python2.6/site-packages/sage/misc/functional.pyc
in symbolic_sum(expression, *args, **kwds)
657 return expression.sum(*args, **kwds)
658 elif len(args) <= 1:
--> 659 return sum(expression, *args)
660 else:
661 from sage.symbolic.ring import SR
TypeError: unsupported operand type(s) for +: 'int' and 'Graph'
Besides, the exception given is odd : addition between int and Graph
types... :-)
Thank youuuuuu !
Nathann
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