Response Handlers

Response handlers are used by Controllers to transform the return value from an action (such as a string, int, etc.) into a suitable webapp2.Response. They provide the convenience of not having to repeat the same code over and over. Ferris provides a couple of built-in response handlers and allows you to register your own.


Simply return a value from a controller’s action:

def test(self):
    return "Hello!"

By returning a string Ferris skips the view and uses whichever response handler is defined for that particular type.


class ferris.core.response_handlers.StringResponseHandler[source]

Simply makes the string the body of the response.

class ferris.core.response_handlers.IntResponseHandler[source]

Returns a response with the specified http status code, for example:

return 404

Will cause a 404 Not Found error response.

class ferris.core.response_handlers.MessageHandler[source]

Returns a Message in JSON format


It’s possible to create new response handlers to handle any type. Simply subclass ResponseHandler like so:

from ferris.core.response_handlers import ResponseHandler
from webapp2 import Response

class WidgetResponseHandler(ResponseHandler):
    type = Widget  # The class that this response handler will deal with.

    # This function is responsible for returning a webapp2.Response
    def process(self, controller, result):
        response = Response()
        response.body =
        return response

Be sure to import this in your controller or in one of the bootstrapping scripts (app/ or app/ to make sure they’re picked up by Ferris.

If you want to preserve the existing response then modify controller.response instead of creating a new one. This preserves headers and other stuff (such as client side caching):

controller.response.body =
return controller.response