What is the best way to repeatedly execute a function in Python?

Question

I am trying to pull some data from a website. The issue I am having is that it pulls the data value and then goes on to just reprint it continuously rather than pull the most recent live data value and update that. I got the code from https://github.com/BitMEX/api-connectors/tree/master/official-ws/python and made a few changes.

from bitmex_websocket import BitMEXWebsocket
import logging
from time import sleep

# Basic use of websocket.
def run():
    logger = setup_logger()

    # Instantiating the WS will make it connect. Be sure to add your api_key/api_secret.
    ws = BitMEXWebsocket(endpoint="https://www.bitmex.com/api/v1", symbol="XBTUSD",
                         api_key=None, api_secret=None)

    logger.info("Instrument data: %s" % ws.get_instrument())

    # Run forever
    while(ws.ws.sock.connected):
        logger.info("Ticker: %s" % ws.get_ticker())
        if ws.api_key:
            logger.info("Funds: %s" % ws.funds())
        #logger.info("Market Depth: %s" % ws.market_depth())
        (logger.info("Recent Trades: %s\n\n" % ws.recent_trades()[0]["size"]))
        sleep(1)


def setup_logger():
    # Prints logger info to terminal
    logger = logging.getLogger()
    logger.setLevel(logging.INFO)  # Change this to DEBUG if you want a lot more info
    ch = logging.StreamHandler()
    # create formatter
    formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
    # add formatter to ch
    ch.setFormatter(formatter)
    logger.addHandler(ch)
    return logger


if __name__ == "__main__":
    run()

Id try disconnecting your socket after the data is logged. Then when you loop through again it will reconnect the socket thus getting the live information — Barb, Oct 22 '19 at 14:57
Have you examined the contents of `ws.recent_trades()`? You're always logging the 0 index of that. If the result is a sequence that is sorted in ascending time series, for instance, you'll may need to log the `ws.recent_trades()[-1]`, I think. — David Zemens, Oct 22 '19 at 15:05

score 1 · Accepted Answer · answered Oct 22 '19 at 15:05

The issue is that your ws.get_ticker() call inside the while loop is not actually getting updated values.

From: https://github.com/BitMEX/api-connectors/blob/febf95659ccd2aa5445e0178c4dbb008d1ae9286/official-ws/python/bitmex_websocket.py#L70

    def get_ticker(self):
        '''Return a ticker object. Generated from quote and trade.'''
        lastQuote = self.data['quote'][-1] # <--SEE HERE. It's just getting the
        lastTrade = self.data['trade'][-1] # information from when the ticker was
                                           # first established.
        ticker = {
            "last": lastTrade['price'],
            "buy": lastQuote['bidPrice'],
            "sell": lastQuote['askPrice'],
            "mid": (float(lastQuote['bidPrice'] or 0) + float(lastQuote['askPrice'] or 0)) / 2
        }

        # The instrument has a tickSize. Use it to round values.
        instrument = self.data['instrument'][0]
        return {k: round(float(v or 0), instrument['tickLog']) for k, v in ticker.items()}

See my comments where lastQuote and lastTrade are defined. You should re-create ws after each loop. You'll have to change the condition in your while loop to while True if you want to do it forever.

from bitmex_websocket import BitMEXWebsocket
import logging
from time import sleep

# Basic use of websocket.
def run():
    logger = setup_logger()




    logger.info("Instrument data: %s" % ws.get_instrument())

    # Run forever    
    while True:
        # Instantiating the WS will make it connect. Be sure to add your api_key/api_secret.
        ws = BitMEXWebsocket(endpoint="https://www.bitmex.com/api/v1", symbol="XBTUSD",
                             api_key=None, api_secret=None)
        logger.info("Ticker: %s" % ws.get_ticker())
        if ws.api_key:
            logger.info("Funds: %s" % ws.funds())
        #logger.info("Market Depth: %s" % ws.market_depth())
        (logger.info("Recent Trades: %s\n\n" % ws.recent_trades()[0]["size"]))
        ws.exit()
        sleep(1)


def setup_logger():
    # Prints logger info to terminal
    logger = logging.getLogger()
    logger.setLevel(logging.INFO)  # Change this to DEBUG if you want a lot more info
    ch = logging.StreamHandler()
    # create formatter
    formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
    # add formatter to ch
    ch.setFormatter(formatter)
    logger.addHandler(ch)
    return logger


if __name__ == "__main__":
    run()

EDIT: Added call to ws.exit() in the while loop to gracefully close ws before opening a new one.

I think this will solve the problem, but it seems like the ticker **should** update itself? (https://github.com/BitMEX/api-connectors/blob/febf95659ccd2aa5445e0178c4dbb008d1ae9286/official-ws/python/bitmex_websocket.py#L188) updates `self.data` when a message is received... but then isn't it the server's responsibility to send that message? — SyntaxVoid, Oct 22 '19 at 15:15

What is the best way to repeatedly execute a function in Python?

1 Answers1