覆盖sqlalchemy反射表中的默认值

I've reflecting a load of tables in an exiting mysql db. I want to express that any columns of a certain name in any table default to datetime.now(). However naively looping through the tables and columns and just setting default on those I find that have a certain name doesn't work, When doing session.add(); session.flush() I get the following error:I've reflecting a load of tables in an exiting