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I want to create a Python app where some data is retrieved and charted on a Dash app.

This is the Dash part. This is where my whole data will be sent and shown on a webpage, since I'm starting now, this is just a basic example of a live chart.

main.py

import dash

from dash.dependencies import Output, Event

import dash_core_components as dcc

import dash_html_components as html

import plotly

import random

import plotly.graph_objs as go

from collections import deque



app = dash.Dash(__name__)

app.layout = html.Div(

    [

        dcc.Graph(id='live-graph', animate=True),

        dcc.Interval(

            id='graph-update',

            interval=1*1000

        ),

    ]

)



@app.callback(Output('live-graph', 'figure'),

             events=[Event('graph-update', 'interval')])

def update_graph_scatter():

    X.append(X[-1]+1)

    Y.append(Y[-1]+Y[-1]*random.uniform(-0.1,0.1))



    data = plotly.graph_objs.Scatter(

            x=list(X),

            y=list(Y),

            name='Scatter',

            mode= 'lines+markers'

            )



    return {'data': [data],'layout' : go.Layout(xaxis=dict(range=[min(X),max(X)]), yaxis=dict(range=[min(Y),max(Y)]),)}



if __name__ == '__main__':

    app.run_server(debug=True)

This is the Python part where the data is retrieved, connecting to a Websocket.
data.py

import websocket

import json

from bitmex_websocket import Instrument

from bitmex_websocket.constants import InstrumentChannels

from bitmex_websocket.constants import Channels



websocket.enableTrace(True)



channels = [

    InstrumentChannels.trade,

]



XBTUSD = Instrument(symbol='XBTUSD',

                    channels=channels)

XBTUSD.on('action', lambda msg: test(msg))



XBTUSD = Instrument(symbol='XBTUSD',                       

                channels=channels)



XBTUSD.on('action', lambda msg: rekter(msg))



def rekter(msg):



    if msg['table'] =='trade':

        Rate = msg['data'][0]['price']



        print(Rate)





XBTUSD.run_forever()

I tried to accomplish that by using imports, so I imported as a module my script, but that didn't work either:

from trades import XBTUSD

import dash

from dash.dependencies import Output, Event

import dash_core_components as dcc

import dash_html_components as html

import plotly

import random

import plotly.graph_objs as go

from collections import deque





X = deque(maxlen=2000)

X.append(1)

Y = deque(maxlen=2000)

Y.append(1)





app = dash.Dash(__name__)

app.layout = html.Div(

    [

        dcc.Graph(id='live-graph', animate=True),

        dcc.Interval(

            id='graph-update',

            interval=1*1000

        ),

    ]

)



@app.callback(Output('live-graph', 'figure'),

              events=[Event('graph-update', 'interval')])

def update_graph_scatter():

    X.append(X[-1]+1)

    Y.append(Y[-1]+Y[-1]*random.uniform(-0.1,0.1))



    data = plotly.graph_objs.Scatter(

            x=list(X),

            y=list(Y),

            name='Scatter',

            mode= 'lines+markers'

            )



    return {'data': [data],'layout' : go.Layout(xaxis=dict(range=[min(X),max(X)]),

                                                yaxis=dict(range=[min(Y),max(Y)]),)}







if __name__ == '__main__':

    app.run_server(debug=True)



XBTUSD.run_forever()

Other than that, I tried turning it into modules, but it didn't work either.

My problem is that I don't know how to "embed" my second part into the first part. I tried do that, but if I put the lineXBTUSD.run_forever()before app.run_server(debug=True) only one part of the code will be executed and my whole Dash app won't run until I stop the first part of the code. Same happens if I do the opposite.

So the problem is XBTUSD.run_forever(), but I can't just remove that line because it won't run data.py. Is there a way to solve this?

I am now thinking of running two separated scripts with one sending data to a DB and the other one should query the DB, retrieve the data and chart it, but I don't know if it's the best solution because a) I'll be handling a lot of data every minute b) I don't know if it'll work when deployed online (on heroku, for example)

The answer is threading or multiprocessing, which will allow both methods to run at the same time. Changes to mutable objects take place in both threads/processes, so you would be able to communicate between your two functions as such. This post provides clarity on the issue.