in

session.query(MyUserClass).filter(MyUserClass.id.in_((123,456))).all()

edit: Without the ORM, it would be

session.execute(
    select(
        [MyUserTable.c.id, MyUserTable.c.name], 
        MyUserTable.c.id.in_((123, 456))
    )
).fetchall()

https://stackoverflow.com/questions/8603088/sqlalchemy-in-clause