Python REST API programming


  • Reusable definitions of REST channels and outgoing connections are first created in the platform's web-based Dashboard before your Python code makes use of them

  • Thanks to this approach, your code focuses exclusively on the business logic instead of dealing with low-level details

Accepting REST calls

  • Use self.request.payload to access input data - it is a dict object created by Zato out of the parsed JSON request
# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class LogInputData(Service):
    """ Logs input data.
    def handle(self):

        # Read input received
        user_id = self.request.payload['user_id']
        user_name = self.request.payload['user_name']

        # Store input in logs'uid:%s; username:%s', user_id, user_name)

Invoke it:

$ curl localhost:11223/api/log-input-data -d '{"user_id":"123", "user_name":"my.user"}'

In server logs:

INFO - uid:123; username:my.user

Calling REST APIs

  • All data can be prepared as dict objects - this includes the payload, query string parameters, path parameters and HTTP headers too

  • Zato will fill in patterns in URL paths, e.g. if the path is /api/billing/{phone_no} then the code below will substitute 271637517 for phone_no and the rest of the parameters will go the query string

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class SetBillingInfo(Service):
    """ Updates billing information for customer.
    def handle(self):

        # Python dict representing the payload we want to send across
        payload = {'billing':'395.7', 'currency':'EUR'}

        # Python dict with all the query parameters, including path and query string
        params = {'cust_id':'39175', 'phone_no':'271637517', 'priority':'normal'}

        # Headers the endpoint expects
        headers = {'X-App-Name': 'Zato', 'X-Environment':'Production'}

        # Obtains a connection object
        conn =['Billing'].conn

        # Invoke the resource providing all the information on input
        response =, payload, params, headers=headers)

        # The response is auto-deserialised for us to a Python dict
        json_dict =

        # Assign the returned dict to our response - Zato will serialise it to JSON
        # and our caller will get a JSON message from us.
        self.response.payload = json_dict

Reacting to REST verbs

  • Implement handle_<VERB> to react to specific HTTP verbs when accepting requests
  • If the service is invoked with a verb that it does not implement, the API client receives status 405 Method Not Allowed
# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class MultiVerb(Service):
    """ Logs input data.
    def handle_GET(self):'I was invoked via GET')

    def handle_POST(self):'I was invoked via POST')

These two will receive HTTP 200:

$ curl -XGET localhost:11223/api/multi-verb -d '{"user_id":"123"}'
$ curl -XPOST localhost:11223/api/multi-verb -d '{"user_id":"123", "user_name":"my.user"}'

But this one will receive HTTP 405:

$ curl -XDELETE localhost:11223/api/multi-verb -d '{"user_id":"123"}'

Choosing REST verbs to call

  • When invoking REST APIs, each connection object has methods representing a specific HTTP verb, e.g. .post, .get, .delete and the others. This means that a single connection object can be used to invoke the same endpoint using multiple verbs.

  • Method .send is an alias to .post

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class MultiVerbCaller(Service):

    def handle(self):

        # Data to send
        payload = {'user_id': '123'}

        # Obtains a connection object
        conn =['REST Endpoint'].conn

        # Invoke the endpoint with POST
        response =, payload)

        # Invoke the endpoint with GET
        response = conn.get(self.cid, payload)

        # Invoke the endpoint with DELETE
        response = conn.delete(self.cid, payload)

        # This is the same as .post
        response = conn.send(self.cid, payload)

Request and response objects

  • All data and metadata is available via self.request and self.response attributes. Security-related details are in

Request object:

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class RequestObject(Service):

    def handle(self):

        # Here is all input data parsed to a Python object

        # Here is input data before parsing, as a string

        # Correlation ID - a unique ID assigned to this request

        # A dictionary of GET parameters

        # A dictionary of POST parameters

        # REST method we are invoked with, e.g. GET, POST, PATCH etc.

        # URL path the service was invoked through

        # Query string and path parameters

        # This is a method, not an attribute,
        # it will return form data in case we were invoked with one on input.
        form_data = self.request.http.get_form_data()

        # Username used to invoke the service, if any

        # A convenience method returning security-related details
        # pertaining to this request.
        sec_info =

Response object:

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ResponseObject(Service):

    def handle(self):

        # Returning responses as a dict will make Zato serialise it to JSON
        self.response.payload = {'user_id': '123', 'user_name': 'my.user'}

        # String data can also be always be returned too,
        # e.g. because you already have data serialised to JSON or to another data format
        self.response.payload = '{"my":"response"}'

        # Sets HTTP status code
        self.response.status_code = 200

        # Sets HTTP Content-Encoding header
        self.response.content_encoding = 'gzip'

        # Sets HTTP Content-Type - note that Zato itself
        # sets it for JSON, you do not need to do it.
        self.response.content_type = 'text/xml; charset=UTF-8'

        # A dictionary of arbitrary HTTP headers to return
        self.response.headers = {
            'Strict-Transport-Security': 'Strict-Transport-Security: max-age=16070400',
            'X-Powered-By': 'My-API-Server',
            'X-My-Header': 'My-Value',

Configuring CORS

  • Implement handle_OPTIONS and set CORS headers as required in your application

  • The actual implementation of the service goes to other methods, handle_POST, handle_GET, as needed by the service

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ConfiguringCORS(Service):

    def handle_POST(self):

        # Actual implementation goes here

    def handle_OPTIONS(self):

        # We only allow requests from this particular origin
        allow_from_name = 'Access-Control-Allow-Origin'
        allow_from_value = ''

        self.response.headers[allow_from_name] = allow_from

Returning responses other than JSON

  • If data assigned to self.response.payload is a string, Zato will never try to serialize it or inspect it in any way. In this manner, you can return any kind of response other than JSON, simply serialize it to string yourself and assign it to self.response.payload.

  • Attribute self.response.content_type can be used to set the correct content type for payload returned

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ServiceCSV(Service):

    def handle(self):

        # We return CSV here
        csv_data = '1,2,3\n4,5,6'

        # Assign data to our response
        self.response.payload = csv_data

        # Let the caller know what we are returning
        self.response.content_type = 'text/csv'

Returning attachments

Use self.response.payload to set the attachment's body and the HTTP Content-Disposition header to signal to clients that you are returning an attachment and to indicate what name it is.

In the example, a static string is returned but the attachment's contents could as well be read from a file, S3, SFTP or any other data source.

# -*- coding: utf-8 -*-

from zato.server.service import Service

class MyService(Service):

    def handle(self):
        self.response.payload = 'Hello, this is an attachment'
        self.response.headers['Content-Disposition'] = 'attachment; filename=hello.txt'

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