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Example code for interpreting the WebSocket API v1 order book feed (synchronous/single-threaded)
Detailed instructions for maintaining a valid order book from a WebSocket API v1 order book feed are available in our How to maintain a valid order book support page.
Example code (in Python) that illustrates the WebSocket API v1 order book logic is provided below and is also available for download as krakenwsorderbook.py.
The example code implements a command line client that subscribes to the specified order book feed, then creates and maintains a valid order book from the feed messages, while outputting the current order book once per second.
The usage of the command line client is ./krakenwsbook.py symbol depth such as the following example commands:
  • •
    ./krakenwsbook.py xbt/usd 10
  • •
    ./krakenwsbook.py ltc/eur 25

Example Code

#!/usr/bin/env python

# Kraken Websocket API Order Book
#
# Usage: ./krakenwsbook.py symbol depth

import sys
import json
import signal
from websocket import create_connection

def alarmfunction(signalnumber, frame):
signal.alarm(1)
api_output_book()

def dicttofloat(keyvalue):
return float(keyvalue[0])

def api_output_book():
bid = sorted(api_book["bid"].items(), key=dicttofloat, reverse=True)
ask = sorted(api_book["ask"].items(), key=dicttofloat)
print("Bid\t\t\t\t\t\tAsk")
for x in range(int(api_depth)):
print("%(bidprice)s (%(bidvolume)s)\t\t\t\t%(askprice)s (%(askvolume)s)" % {"bidprice":bid[x][0], "bidvolume":bid[x][1], "askprice":ask[x][0], "askvolume":ask[x][1]})

def api_update_book(side, data):
for x in data:
price_level = x[0]
if float(x[1]) != 0.0:
api_book[side].update({price_level:float(x[1])})
else:
if price_level in api_book[side]:
api_book[side].pop(price_level)
if side == "bid":
api_book["bid"] = dict(sorted(api_book["bid"].items(), key=dicttofloat, reverse=True)[:int(api_depth)])
elif side == "ask":
api_book["ask"] = dict(sorted(api_book["ask"].items(), key=dicttofloat)[:int(api_depth)])

signal.signal(signal.SIGALRM, alarmfunction)

if len(sys.argv) < 3:
print("Usage: %s symbol depth" % sys.argv[0])
print("Example: %s xbt/usd 10" % sys.argv[0])
sys.exit(1)

api_feed = "book"
api_symbol = sys.argv[1].upper()
api_depth = sys.argv[2]
api_domain = "wss://ws.kraken.com/"
api_book = {"bid":{}, "ask":{}}

try:
ws = create_connection(api_domain)
except Exception as error:
print("WebSocket connection failed (%s)" % error)
sys.exit(1)

api_data = '{"event":"subscribe", "subscription":{"name":"%(feed)s", "depth":%(depth)s}, "pair":["%(symbol)s"]}' % {"feed":api_feed, "depth":api_depth, "symbol":api_symbol}

try:
ws.send(api_data)
except Exception as error:
print("Feed subscription failed (%s)" % error)
ws.close()
sys.exit(1)

while True:
try:
api_data = ws.recv()
except KeyboardInterrupt:
ws.close()
sys.exit(0)
except Exception as error:
print("WebSocket message failed (%s)" % error)
ws.close()
sys.exit(1)
api_data = json.loads(api_data)
if type(api_data) == list:
if "as" in api_data[1]:
api_update_book("ask", api_data[1]["as"])
api_update_book("bid", api_data[1]["bs"])
signal.alarm(1)
elif "a" in api_data[1] or "b" in api_data[1]:
for x in api_data[1:len(api_data[1:])-1]:
if "a" in x:
api_update_book("ask", x["a"])
elif "b" in x:
api_update_book("bid", x["b"])

ws.close()
sys.exit(1)