You have to add `nullable=False` to these columns and provide a `server_default` parameter (because the `default` parameter is ignored in Alembic. Then you have to amend the column again to remove `server_default`. Here is how I did it in Lastuser:

https://github.com/hasgeek/lastuser/blob/master/alembic/versions/25e7a9839cd4_user_status_flag.py#L19