Python example WebSocket API

mehdi.el.hamzaoui

Hi,

I would like to run the Python example for market price from the streamingtools folder.

Let's take this function:

def process_message(ws, message_json):
""" Parse at high level and output JSON of message """
message_type = message_json['Type']

........

What do the arguments "ws" and message_json" entail here? What should I input there?

Thanks in advance

umer.nalla

Hi @mehdi.el.hamzaoui

If you have not already done so, I recommend you work through the Quick Start guide for Websocket API.

There are two versions of the Quick Start - one for connecting to your TREP / ADS and for a Elektron Cloud connection - please refer to the appropriate one.

Before referring to the streamingtools examples, it may better to have a play around with the WebSocket API Try it Now! Documentation - as this will allow to easily understand the different JSON request messages you can use to login, request data - as well as the JSON responses you can receive from the server.

It may also be worth referring to the documentation for the python websocket client documentation - if you are not familiar with how the python Websocket library works. The process_message method you refer to is actually called from the on_message method which is a callback handler specified when creating the WebSocketApp, to handle any incoming messages from the Websocket connection.

If you follow the streamingtools example code flow, you will see that it creates a websocket connection and specifies various callback handlers e.g. on_message, on_open etc.

Once the connection is open, the on_open method calls the send_login_request method to send a login request to the server.

When a message is received back from the server, the on_message method dumps the JSON response and calls the process_message method, which checks for a valid login response and if so, it then calls the process_login_response method which simply sends a data request to the server - requesting 'TRI.N' MarketPrice data.

Assuming the server responds (asynchronously) with data, the on_message method is called again which dumps the data (JSON payload) to the console.

As the data request is by default a streaming request, the on_message method will be called asynchronously as and when their is market activity and the server sends updates over the websocket connection.

You will note that the process_message method also checks each message received for a Ping and if so, responds with a Pong. This ensures the heartbeat is maintained with the server and the connection is kept alive.