text: from sqlalchemy import *
  from migrate import *
  
  
  from migrate.changeset import schema
  pre_meta = MetaData()
  post_meta = MetaData()
  
  def upgrade(migrate_engine):
      # Upgrade operations go here. Don't create your own engine; bind
      # migrate_engine to your metadata
      pre_meta.bind = migrate_engine
      post_meta.bind = migrate_engine
  
  
  def downgrade(migrate_engine):
      # Operations to reverse the above upgrade go here.
      pre_meta.bind = migrate_engine
      post_meta.bind = migrate_engine
  