#4954: Words_over_Alphabet should check the type of input alphabet
---------------------------+------------------------------------------------
Reporter: slabbe | Owner: mhansen
Type: defect | Status: new
Priority: major | Milestone: sage-3.4
Component: combinatorics | Keywords: words alphabet
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Do
{{{
sage: W=Words('ab')
sage: W.alphabet?
}}}
and you get the following help example :
{{{
sage: from sage.combinat.words.words import Words_over_Alphabet
sage: W = Words_over_Alphabet([1,2,3])
sage: W.alphabet()
[1, 2, 3]
sage: from sage.combinat.words.words import OrderedAlphabet
sage: W = Words_over_Alphabet(OrderedAlphabet('ab'))
sage: W.alphabet()
Ordered Alphabet ['a', 'b']
}}}
The first of the above example is misleading. In fact, it is not usable :
{{{
sage: from sage.combinat.words.words import Words_over_Alphabet
sage: W = Words_over_Alphabet([1,2,3])
sage: W.alphabet()
[1, 2, 3]
sage: W([1,1,1,2,1,3])
Traceback (most recent call last):
...
AttributeError: 'list' object has no attribute 'rank'
}}}
The problem comes from the fact that Words_over_Alphabet doesn't check the
input alphabet before asigning it to self._alphabet(). It should either do
{{{alphabet=OrderedAlphabet(alphabet)}}} before or check the type of the
input alphabet with a isinstance.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4954>
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