Response objects


All services produce responses through their self.response attribute. Unlike with requests, there are no protocol-specific sub-attributes.

The most general way to create a response, and one that is always possible, is to assign a string or Unicode object to self.response.payload, e.g. as a result of manual serialization.

However, if using SimpleIO or if a channel's definition is JSON or XML, it is also possible for Zato to serialize objects directly, e.g. from dicts or SQLAlchemy objects.

Response attributes

All of the attributes and methods are always available to all services, regardless of the protocol they are invoked through though in the case of HTTP-specific ones, using them will be a no-op if the service is not invoked through HTTP.

Attribute Description
self.response The main attribute via which responses are produced
self.response.payload The object to which responses are assigned, i.e. this is the attribute through which a service's business data is returned, such as a JSON message
self.response.status_code (HTTP only) An integer status code such as 200 or 401 to return in response
self.response.content_encoding (HTTP only) Sets response's Content-Encoding header value
self.response.content_type (HTTP only) Sets response's Content-Type header value
self.response.headers (HTTP only) A dictionary of header name/value to set in the response


Assiging to self.response.payload lets one return responses from services. It can be done in several ways:

By assigning a string/unicode object directly. This approach is always available:

def handle(self):
    self.response.payload = '{"id":123, "name":"John Doe"}'

If using SimpleIO, all the attributes can be assigned to as they appear in the SimpleIO definition, either one, as a dictionary or as a list. Serialization to JSON or XML will be done by Zato automatically, depending on service's channel definition.

def handle(self):
    self.response.payload = {'id':123, 'name':'John Doe'}
To return a list of objects, attach it to self.response.payload, as above:

def handle(self):
    data = [
        {'id':123, 'name': 'John Doe'},
        {'id':456, 'name': 'Jane Xi'},
    self.response.payload = data

Assigning attributes individually:

def handle(self): = 123 = 'John Doe'

If using SimpleIO, it is also possible to assign SQLAlchemy objects directly from an SQL query:

  def handle(self):

      # Get user from database
      user = session.query(UserModel).\

      # Assign the user object directly to response
      self.response.payload = user


  • Consult the dedicated chapter with programming examples for more details.
  • To learn more about SimpleIO, click here
  • Visit this chapter to read more about request objects