One of the first things that you learn in programming classes is that nobody can get a complex program right the very first time. Software evolves over time, and we hope for the best. Automation in automated testing helps ensure that our programs improve over time. However, when it comes to evolving database schemas, automation doesn't seem to be so obvious. Especially in large enterprises, database schemas are the domain of database administrators and specialists. Of course, there are security and operational issues related to changing schemas, even more so in production databases. In any case, you can always implement database migration in your local test environment and document proposed changes for the production team.
We will use Alembic to demonstrate how you can go about setting up migration scripts. In my opinion, Alembic is the right tool for the job, although it is in beta as of September 2015.