exceptions.py 文件源码

def __str__(self):
        lines = []
        self.errors.sort(key=lambda e: e.order)
        for cls, errors_of_cls in groupby(self.errors, lambda e: e.__class__):
            lines.append(cls.head)
            lines.extend(e.body() for e in errors_of_cls)
        if lines:
            return '\n'.join(lines)