save log to file
        Returns:

def save_log(self, filename = None):
        """
        save log to file
        Returns:

        """
        if filename is None:
            filename = self.filename('-info.txt')
        filename = self.check_filename(filename)
        # filename = self.check_filename(filename)
        # windows can't deal with long filenames so we have to use the prefix '\\\\?\\'
        # if len(filename.split('\\\\?\\')) == 1:
        #     filename = '\\\\?\\' + filename
        with open(filename, 'w') as outfile:
            for item in self.log_data:
                outfile.write("%s\n" % item)