I don't have any personal experience with sqlalchemy-migrate, but here's a tutorial:
http://caneypuggies.alwaysreformed.com/wiki/DevelopingWithMigrations
If you use the scripts mentioned there, you can create migrations like this:
./new_migration.sh "Describe the new migration here"
I do all my migrations with South: http://south.aeracode.org/
Note that it depends on the Django framework though.