Accessing incoming messages with a Python websocket client

Question

I am trying to receive messages via websocket-client module and be able to use received messages for other purposes (e.g. execute buy/sell orders based on incoming messages).

Here is what I have so far:

import websocket
import time
import json

def on_message(ws, message):
    try:
        current_price = json.loads(message)
        print(current_price["price"])       # data type is dict.. only showing values for the key 'price'

    except:
        print("Please wait..")
        time.sleep(1)          

def on_error(ws, error):
    print(error)


def on_close(ws):
    print("### closed ###")


def on_open(ws):
    sub_params = {'type': 'subscribe', 'product_ids': ['BTC-USD'], 'channels': ['ticker']}
    ws.send(json.dumps(sub_params))

if __name__ == "__main__":
    websocket.enableTrace(False)
    ws = websocket.WebSocketApp("wss://ws-feed.pro.coinbase.com/",
                              on_open = on_open,
                              on_message = on_message,
                              on_error = on_error,
                              on_close = on_close)

    ws.run_forever()

Running this code will print the current Bitcoin price (current_price) as they come in through its websocket feed.

What I want to do next is to be able to access that variable current_price outside of the websocket function, and I am having a difficulty here. Writing anything beyond ws.run_forever() will be ignored because the websocket event loop will never end.

So I tried running the websocket on a separate thread with ‘threading’ mordule:

    import websocket
  import json
  import threading

  current_price = 0

  def on_message(ws, message):

      global current_price
      current_price = message

  def on_error(ws, error):
      print(error)

  def on_close(ws):
      print("### closed ###")


  def on_open(ws):
      sub_params = {'type': 'subscribe', 'product_ids': ['BTC-USD'], 'channels': ['ticker']}
      ws.send(json.dumps(sub_params))

  if __name__ == "__main__":
      websocket.enableTrace(False)
      ws = websocket.WebSocketApp("wss://ws-feed.pro.coinbase.com/",
                                on_open = on_open,
                                on_message = on_message,
                                on_error = on_error,
                                on_close = on_close)

      ws_thread = threading.Thread(target = ws.run_forever)
      ws_thread.start()
      print(current_price)

and this returns 0. What can I do to make this work?

Asked By: Chobani

||

Source

Answer 1

Not sure if this is the most appropriate answer, but found a way to make this work.

import queue
.
.
.
.

    def on_message(ws, message):
            current_price = message
            q.put(current_price)
    .
    .
    .

    ws_thread.start()

    while True:
        print(q.get())

Answered By: Chobani

Answer 2

I’ve worked it out. The key to is is to use functools partials to wrap the callback functions. I’ve built a simple multithreaded demonstrator:

from websocket import WebSocketApp
import time
from threading import Thread
from queue import Queue
from functools import partial

class websocket_client:
    def __init__(self):
        self.responseQ = Queue() #our message response Q
        #add the response Qs on by wrapping the callbacks in functools partials
        self.websocket = WebSocketApp("ws://echo.websocket.events",
                                on_open = partial(self.on_open, responseQ=self.responseQ),
                                on_message = partial(self.on_message, responseQ=self.responseQ),
                                on_error = partial(self.on_error, responseQ=self.responseQ),
                                on_close = partial(self.on_close, responseQ=self.responseQ))
        # start run_forever as thread. request keep alive pings every 10 seconds with 5 second timouts
        self.controller = Thread(target=self.websocket.run_forever, args=(None, None, 10, 5))
        self.controller.start()
    
    def on_open(self, websocket, responseQ):
        #print("Opening Connection (run_forever)")
        responseQ.put("Connected") #transmit status information
    
    def on_error(self, websocket, error, responseQ):
        #print("Connection Error (run_forever):", error)
        responseQ.put(error) # or error messages

    def on_message(self, websocket, message,  responseQ):
        #print("Message Received (run_forever):", message)
        responseQ.put(message)
    
    def on_close(self, websocket, status, message, responseQ):
        #print("Closing Connection (run_forever):", status, message)
        responseQ.put({'status': message, 'message': message}) #send close status and message in a dictionary
    

if __name__ == '__main__':
    client = websocket_client() # make the client
    while client.responseQ.get() != "Connected": time.sleep(0.1) #block until connected
    print("nSERVER GREETING:", client.responseQ.get()) #greeting from server
    while True:
        message_to_send = time.strftime("%b %d %Y %H:%M:%S")
        client.websocket.send(message_to_send)
        message_received = client.responseQ.get()
        print("Main Thread: SENT --> '%s' RECEIVED --> '%s'" %(message_to_send, message_received))
        time.sleep(1)

Answered By: David Megson-Smith

Accessing incoming messages with a Python websocket client

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