Build and return the data line

def build_data(self, plugin, attribute, stat):
        """Build and return the data line"""
        line = ''

        if attribute is not None:
            line += '{}{}'.format(str(stat.get(attribute, self.na)),
                                  self.separator)
        else:
            if isinstance(stat, dict):
                for v in stat.values():
                    line += '{}{}'.format(str(v), self.separator)
            elif isinstance(stat, list):
                for i in stat:
                    if isinstance(i, dict) and 'key' in i:
                        for v in i.values():
                            line += '{}{}'.format(str(v), self.separator)
            else:
                line += '{}{}'.format(str(stat), self.separator)

        return line