Use automap_base to use an existing db with sqlalchemy

read_postgres_sqlalchemy.py

from sqlalchemy import MetaData, create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.automap import automap_base
from sqlalchemy.sql import select
from sqlalchemy import func

engine = create_engine('postgres://db_user@db_host:5432/db_name', client_encoding='utf8')
Session = sessionmaker(bind=engine)
session = Session()

metadata = MetaData()
metadata.reflect(engine, only=['table_name1', 'table_name2'])
Base = automap_base(metadata=metadata)
Base.prepare()

TableName1, TableName2 = Base.classes.table_name1, Base.classes.table_name2

s = select([TableName1]).where(TableName1.id > 1)
second_row_id = session.execute(s).scalar()

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