convert text into typecode specific data.

def text_to_data(self, text, elt, ps):
        '''convert text into typecode specific data.
        '''
        v = text
        if self.pyclass is not None:
            return self.pyclass(v)

        m = _magicnums.get(v)
        if m: return m

        try:
            return float(v)
        except:
            raise EvaluateException('Unparseable floating point number',
                    ps.Backtrace(elt))