SQLAlchemy - не строится схема

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Boolean, ForeignKey

Base = declarative_base()


class Gateway(Base):
    __tablename__ = 'gateway'

    id = Column(Integer, autoincrement=True, primary_key=True)
    implementation = Column(String, nullable=False)
    marker_active = Column(Boolean, nullable=False, default=False)

print Gateway.__table__

>>> User.__table__ 
Table('users', MetaData(bind=None),
            Column('id', Integer(), table=<users>, primary_key=True, nullable=False),
            Column('name', String(), table=<users>),
            Column('fullname', String(), table=<users>),
            Column('password', String(), table=<users>), schema=None)