example.py

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import (declarative_base, declared_attr,
    AbstractConcreteBase)


engine = create_engine('sqlite://', echo=True)
Base = declarative_base()
Base.metadata = MetaData()


class CommonMetadata(Base):
    __tablename__ = 'metadata'

    @declared_attr
    def id(cls):
        return Column(
            Integer,
            primary_key=True,
        )

    data = Column(Text)


class Product(AbstractConcreteBase, Base):
    @declared_attr
    def id(cls):
        return Column(
            Integer,
            ForeignKey(
                'metadata.id',
                deferrable=True,
                initially="DEFERRED",
            ),
            primary_key=True,
        )


class Electronics(Product):
    __tablename__ = 'electronics'

    clock_speed = Column(Numeric)

    __mapper_args__ = {
        'polymorphic_identity': 'electronics',
        'concrete': True
    }


class Clothing(Product):
    __tablename__ = 'clothing'

    __mapper_args__ = {
        'polymorphic_identity': 'clothing',
        'concrete': True
    }

    size = Column(Integer)



configure_mappers()

Base.metadata.create_all(engine)