python - Handling duplicates in SQLAlchemy -

i using sqlalchemy write data python database in sql. use code below write contents of 1 of tables sql, give me primary keys first table, table 1, use when writing in data next table, table 2 foreign keys of table 2 mapped table 1. however, writing function prevent duplicated data being written these tables if run script again.

base.metadata.create_all(engine, checkfirst=true) session = sessionmaker(bind=engine) session = session(bind=engine, expire_on_commit=false) # writing data table 1 session.add_all([ table1(name = 'euro'), table1(name = 'fed'), table1(name = 'aus'), table1(name = 'boe'), table1(name = 'canada')])  session.flush() session.commit() session = session(bind=engine, expire_on_commit=false)      #obtaining primary keys table 1 listofindices = []  row in session.query(table 1):     listofindices.append(row.id) 

so, far code handling duplicates follows. however, not sure how obtain primary keys table 1 , @ same time prevent duplicated data being written it:

session = scoped_session(sessionmaker(bind=engine)) s = session() select_statement = s.execute('select count(*) table 1') result = select_statement.fetchone() table_exists = result[0] #does table 1 exist? if table_exists != 0:     #dont know write here prevent duplicates table exists