python学习笔记1-元类__metaclass__

class Foo(Bar):
　　def __init__():
　　　　pass

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class HotWordType(Base):
    # 表名称
    __tablename__ = ‘hotWordType‘
    # id typeName
    id = Column(Integer, primary_key=True)  # 主键
    typeName = Column(String(20), nullable=False)  # 类型名
    hotWord = relationship(‘HotWord‘, backref=‘hotWordType‘)

The new base class will be given a metaclass that produces
appropriate :class:`~sqlalchemy.schema.Table` objects and makes
the appropriate :func:`~sqlalchemy.orm.mapper` calls based on the
information provided declaratively in the class and any subclasses
of the class.

class DeclarativeMeta(type):
    def __init__(cls, classname, bases, dict_):
        if ‘_decl_class_registry‘ not in cls.__dict__:
            _as_declarative(cls, classname, cls.__dict__)
        type.__init__(cls, classname, bases, dict_)

    def __setattr__(cls, key, value):
        _add_attribute(cls, key, value)