How to simulate data and change the dcc.Interval component without using global variables?

Dash Python
1

I’m building a dash app that displays real time data in a table. Since the real time data is not yet available I want to simulate the data myself, using the dcc.Interval component. Please consider the following code:

import dash
import dash_core_components as dcc
import dash_html_components as html
import dash_table_experiments as dte
import pandas as pd
from random import randint, uniform

app = dash.Dash()
interval_state = 1000

live_data = pd.DataFrame({
    'Column 1': ['start'],
    'Column 2': ['start']
})

app.layout = html.Div(
    html.Div([
        html.Button(
            'Pause/Continue',
            id = 'pause-button',
        ),
        dte.DataTable(
            id = 'data-table',
            rows = [{}],
            sortable = True,
            filterable = True,
            editable = True,
        ),
        dcc.Interval(
            id = 'interval-component',
            interval = 3*interval_state
        )
    ])
)

@app.callback(
    dash.dependencies.Output('data-table','rows'),
    events = [dash.dependencies.Event('interval-component', 'interval')]
)
def update_table():
    global live_data
    new_data = pd.DataFrame({
        'Column 1': [randint(0,10)],
        'Column 2': [uniform(0,1)]
    })
    live_data = pd.concat([new_data, live_data])
    return live_data.to_dict('Records')

@app.callback(
    dash.dependencies.Output('interval-component','interval'),
    [dash.dependencies.Input('pause-button','n_clicks')]
)
def update_interval_length(n_clicks):
    global interval_state
    if interval_state == 1000:
        interval_state = 1000*60
        return interval_state
    else:
        interval_state = 1000
        return interval_state

if __name__ == '__main__':
    app.run_server(debug=True)

I think this script works fine. I’ve written the update_interval_length function so that I can pause the input to filter the data. The dash guide warns that global variables will break you app though and I would like to know if there’s a way to simulate data and pause the Interval component without using global variables. Is there for instance a way to run another python script that can be used as an external source for the app?

2

Thanks for writing in. You’re right to be leery of global variables, but since this is meant to be a POC for your actual live app, you should be ok.

To really avoid using global variables I would create a toy front end that mimics what your live data will ultimately look like. A few examples could include a lightweight flask server that calculates time-based data, or a python script tied to a cron job that updates a lightweight database. If you know what your live data backend is going to look like, you could design a toy version that mimics its architecture.

3

I used a flask app, thanks for the tip!