Check out example codes for "sqlalchemy sequence postgresql". It will help you in understanding the concepts better.

Code Example 1

#!/usr/bin/env python

from sqlalchemy import create_engine, Column, Integer, String, Sequence
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()
USER_ID_SEQ = Sequence('user_id_seq')  # define sequence explicitly
class User(Base):
    __tablename__ = 'users'
    # use sequence in column definition, and pass .next_value() as server_default
    id = Column(Integer, USER_ID_SEQ, primary_key=True, server_default=USER_ID_SEQ.next_value())
    name = Column(String(50))
    fullname = Column(String(50))
    password = Column(String(12))

    def __repr__(self):
        return "<User(name='%s', fullname='%s', password='%s')>" % (
                                self.name, self.fullname, self.password)

db_url = 'postgresql://localhost/serial'
engine = create_engine(db_url, echo=True)
Base.metadata.create_all(engine)

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