code: def compile(self, name, migrate='', rollback='', num=None):
          
          if num is None:
              num = len(self.todo)
  
          name = '{:03}_'.format(num + 1) + name
          filename = name + '.py'
          path = os.path.join(self.migrate_dir, filename)
          with open(path, 'w') as f:
              f.write(MIGRATE_TEMPLATE.format(migrate=migrate, rollback=rollback, name=filename))
  
          return name
docs: Create a migration.