Looks up the exception in error_dictionary and raises it.
        Required arguments:
        * ncode - Error numerical code.

def exception(self, ncode):
        """
        Looks up the exception in error_dictionary and raises it.
        Required arguments:
        * ncode - Error numerical code.
        """
        error = self.error_dictionary[ncode]
        error_msg = self._buffer[self._index - 1].split(None, 3)[3]
        exec('raise self.%s("%s: %s")' % (error, error, error_msg))