convert text into typecode specific data.

def text_to_data(self, text, elt, ps):
        '''convert text into typecode specific data.
        '''
        if text is None:
            return None
        m = Duration.lex_pattern.match(text)
        if m is None:
            raise EvaluateException('Illegal duration', ps.Backtrace(elt))
        d = m.groupdict()
        if d['T'] and (d['h'] is None and d['m'] is None and d['s'] is None):
            raise EvaluateException('Duration has T without time')
        try:
            retval = _dict_to_tuple(d)
        except ValueError, e:
            raise EvaluateException(str(e))
    
        if self.pyclass is not None:
            return self.pyclass(retval)
        return retval