code: def _get(self, instance, **kw):
          
          logger.debug("ATFieldManager::get: instance={} field={}"
                       .format(instance, self.field))
  
          # check the field permission
          if not self.field.checkPermission("read", instance):
              raise Unauthorized("You are not allowed to read the field {}"
                                 .format(self.name))
  
          # return the field value
          return self.field.get(instance)
docs: Get the value of the field