docs: def _dispatch_gen(self):
          """
          Process the generate subset of commands.
          """
  
          if not os.path.isdir(self._args.output):
              raise exception.Base("%s is not a writeable directory" % self._args.output)
  
          if not os.path.isfile(self._args.models_definition):
              if not self.check_package_exists(self._args.models_definition):
                  raise exception.Base("failed to locate package or models definitions file at: %s" % self._args.models_definition)
  
          from prestans.devel.gen import Preplate
          preplate = Preplate(
              template_type=self._args.template,
              models_definition=self._args.models_definition,
              namespace=self._args.namespace,
              filter_namespace=self._args.filter_namespace,
              output_directory=self._args.output)
  
          preplate.run()