Writes case data to file in MATPOWER format.

def write(self, file_or_filename):
        """ Writes case data to file in MATPOWER format.
        """
        if isinstance(file_or_filename, basestring):
            self._fcn_name, _ = splitext(basename(file_or_filename))
        else:
            self._fcn_name = self.case.name

        self._fcn_name = self._fcn_name.replace(",", "").replace(" ", "_")

        super(MATPOWERWriter, self).write(file_or_filename)