# model1.py
# coding: utf-8
from sqlalchemy import Column, INTEGER, String, DATETIME, FLOAT, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
BASE = declarative_base()
class Model1(BASE):
    __tablename__ = 'model1'
    id = Column(INTEGER, primary_key=True, nullable=False)
    model2_ids = relationship('Model2')

# model2.py
# coding: utf-8
from sqlalchemy import Column, INTEGER, String, DATETIME
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
BASE = declarative_base()
class Model2(BASE):
    __tablename__ = 'model2'
    id = Column(INTEGER, primary_key=True, nullable=False)
    model1_id = Column(INTEGER, ForeignKey('model1.id'))

# coding: utf-8
from sqlalchemy import MetaData, String, Table, Column, INTEGER, FLOAT, DATETIME
from migrate.changeset.constraint import ForeignKeyConstraint
meta = MetaData()
table1 = Table(
    'model1', meta,
    Column('id', INTEGER, primary_key=True, nullable=False),
    mysql_charset='utf8'
)
table2 = Table(
    'model2', meta,
    Column('id', INTEGER, primary_key=True, nullable=False),
    Column('model1_id', INTEGER),
    mysql_charset='utf8'
)
fkey = ForeignKeyConstraint(
    columns=[table2.c.model1_ids],
    refcolumns=[table1.c.id]
)
def upgrade(migrate_engine):
    meta.bind = migrate_engine
    table1.create()
    table2.create()
    fkey.create()
def downgrade(migrate_engine):
    meta.bind = migrate_engine
    table1.drop()
    table1.drop()
    fkey.drop()

model2_ids = relationship('Model2')

sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper|VMInstance|vminstance, expression 'Model2' failed to locate a name ("name 'Model2' is not defined"). If this is a class name, consider adding this relationship() to the <class '...'> class after both dependent classes have been defined.   

model2_ids = relationship(Model2)

sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column 'model2.model1_ids' could not find table 'model1' with which to generate a foreign key to target column 'id' 

model2_ids = relationship('Model2')

mysql://user:passw@localhost/db_name

When initializing mapper Mapper|VMInstance|vminstance, expression 'Model2' failed to locate a name ("name 'Model2' is not defined").