Check if the provided file is a valid file for this plugin.

        :arg filename: the path to the file to check.

def valid_file(cls, filename):
        """ Check if the provided file is a valid file for this plugin.

        :arg filename: the path to the file to check.

        """
        file_ex = os.path.splitext(filename)[1].replace('.', '', 1)
        return file_ex in SUPPORTED_FILES and is_excel_file(filename)