我正在同时尝试2种新事物，因此在简化和阐明方面均提供了帮助。

from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy import Column, Float, event

class TimeStampMixin(object):

    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()

    created = Column(Float)
    modified = Column(Float)
    def __init__(self, created = None,
                       modified = None):
        self.created = created
        self.modified = modified

def create_time(mapper, connection, target):
    target.created = time()

#def modified_time(mapper, connection, target):
#    target.modified = time()

event.listen(TimeStampMixin, 'before_insert', create_time)
#event.listen(TimeStampMixin, 'before_update', modified_time)

所以我想创建一个mixin，可以在任何课程中应用：

class MyClass(TimeStampMixin, Base):
    etc, etc, etc

此类继承了在创建时创建时间戳并在更新时创建/修改时间戳的功能。

导入时出现此错误：

raise exc.UnmappedClassError(class_)
sqlalchemy.orm.exc.UnmappedClassError: Class 'db.database.TimeStampMixin' is not mapped

在这一点上，我很沮丧。