lightweight database migration tool for SQLAlchemy - Python module

 Alembic is a new database migration tool, written by the author
 of SQLAlchemy. A migration tool offers the following functionality:
 .
  * Can emit ALTER statements to a database in order to change the
    structure of tables and other constructs
  * Provides a system whereby "migration scripts" may be constructed;
    each script indicates a particular series of steps that can
    "upgrade" a target database to a new version, and optionally a
    series of steps that can "downgrade" similarly, doing the same
    steps in reverse.
  * Allows the scripts to execute in some sequential manner.