1. 安装必要的依赖：

$ pip install sqlalchemy sqlalchemy-utils psycopg2 alembic

2. 创建两个表以及它们之间的联接表：

from sqlalchemy import create_engine, Table, Column, Integer, ForeignKey
from sqlalchemy.orm import relationship, backref
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

association_table = Table('association', Base.metadata,
    Column('left_id', Integer, ForeignKey('left.id')),
    Column('right_id', Integer, ForeignKey('right.id'))
)

class Left(Base):
    __tablename__ = 'left'

    id = Column(Integer, primary_key=True)
    rights = relationship(
        'Right',
        secondary=association_table,
        backref=backref('lefts', lazy='dynamic')
    )

class Right(Base):
    __tablename__ = 'right'

    id = Column(Integer, primary_key=True)

engine = create_engine('postgres://localhost/mydatabase')
Base.metadata.create_all(engine)

3. 使用alembic生成迁移脚本：

$ alembic init alembic

4. 修改alembic/env.py配置文件用于支持sqlalchemy_utils：

# ...之前的代码
from alembic import context

# 新增如下两行
from sqlalchemy_utils import database_exists, create_database

# ...之后的代码
def run_migrations_offline():
    # ...之前的代码
    url = config.get_main_option("sqlalchemy.url")
    if not database_exists(url):
        create_database(url)
    # ...之后的代码

5. 编写迁移脚本：

$ alembic revision --autogenerate -m "create tables"

将自动生成如下的迁移脚本：

from alembic import op
import sqlalchemy as sa


# revision identifiers, used by Alembic.
revision = 'a5ddc2b0f7f8'
down_revision = None
branch_labels = None
depends_on = None


def upgrade():
    # ### commands auto generated by Alembic - please