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I'm looking for ways to visualize tick data and put it on a website. I've came across the below methods that have clear limitations.

I am aware that it's possible with node.js libraries but I dont want javascript at all because a) I hate JS as a language, b) d3.js it seems like a overkill for a small project.

Plotly + dash can host real time python applications but foundationally it only support interval updates, not tick updates. It is possible to hack it by setting update function to high frequency but I'm looking for a solution designed for this specific application. This would be my fallack soln if nothing better comes up.

I also came across articles that describes using matplotlib.animations, but I am not aware of a way to put matplotlib live feed on a server website.

Some other articles describe exporting images daily with matplotlib which I find as an abusive usage of the term realtime.

Finally, Python only please.

smaillis
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    For any asynchronic task you will need you user a 3rd party service like redis or rabbitmq and in Pyhton you should user celecry – Nir Elbaz Jan 05 '21 at 12:03

1 Answers1

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One option would be to use a websocket to stream the data. You could use e.g. the WebSocket component in dash-extensions==0.0.41. Here is a small example,

import json
import dash_html_components as html
import random
import dash_core_components as dcc
import plotly.graph_objects as go
from gevent import sleep
from dash import Dash
from dash.dependencies import Input, Output, State
from dash_extensions import WebSocket
from dash_extensions.websockets import SocketPool, run_server


# Generator to simulate continuous data feed.
def data_feed():
    while True:
        sleep(random.uniform(0, 2))  # delay between data events
        yield random.uniform(0, 1)  # the data value


# This block runs asynchronously.
def ws_handler(ws):
    for data in data_feed():
        ws.send(json.dumps(data))  # send data


# Create example app.
app = Dash(prevent_initial_callbacks=True)
socket_pool = SocketPool(app, handler=ws_handler)
app.layout = html.Div([dcc.Graph(id="graph", figure=go.Figure(go.Scatter(x=[], y=[]))), WebSocket(id="ws")])


@app.callback(Output("graph", "figure"), [Input("ws", "message")], [State("graph", "figure")])
def update_graph(msg, figure):
    x, y = figure['data'][0]['x'], figure['data'][0]['y']
    return go.Figure(data=go.Scatter(x=x + [len(x)], y=y + [float(msg['data'])]))


if __name__ == '__main__':
    run_server(app, port=5000)  # 5000 if the default port

Disclaimer: I am the author of dash-extensions.

emher
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  • I'm trying to replace the data feed with a queue that receives data from another thread, but for some reason ws.send ranned but it never calls the update_graph function so the graph never updates. Do you know why? threading.Thread(target = genData,daemon =True, args = (q,) ).start() ... socket_pool = SocketPool(app, handler=lambda x: ws_handler(x,q)) ... def ws_handler(ws,q): # for data in data_feed(): # ws.send(json.dumps(data)) # send data while len(list(q.queue))!=0: data = q.get() ws.send(json.dumps(data)) q.task_done() – smaillis Jan 09 '21 at 02:09