Yesterday I published dbupgrade, a simple database migration tool, written in Python. It allows you to put database migration files (simple SQL files with a special header) into a directory and upgrade your database schema. While this is a new project, it was extracted from an internal library I’ve been using for years and should work fairly reliably for MySQL/MariaDB and Postgres databases.
dbupgrade is available at github and at pypi or via pip: pip install dbupgrade.