convert text into typecode specific data.

def text_to_data(self, text, elt, ps):
        '''convert text into typecode specific data.
        '''
        prefix,localName = SplitQName(text)
        nsdict = ps.GetElementNSdict(elt)
        prefix = prefix or ''
        try:
            namespaceURI = nsdict[prefix]
        except KeyError, ex:
            raise EvaluateException('cannot resolve prefix(%s)'%prefix,
                ps.Backtrace(elt))
                
        v = (namespaceURI,localName)
        if self.pyclass is not None:
            return self.pyclass(v)    
        return v