mytable = Table('mytable', meta, Column('customer_id', Integer, ForeignKey(
    'customers.customer_id')), Column('location_code', Unicode(10)),
    UniqueConstraint('customer_id', 'location_code', name='uix_1'))
Index('myindex', mytable.c.customer_id, mytable.c.location_code, unique=True)


class Location(Base):
    __tablename__ = 'locations'
id = Column(Integer, primary_key=True)
customer_id = Column(Integer, ForeignKey('customers.customer_id'), nullable
    =False)
location_code = Column(Unicode(10), nullable=False)
__table_args__ = UniqueConstraint('customer_id', 'location_code', name=
    '_customer_location_uc'),
sqlalchemy unique across multiple columns