Sharing data between callbacks in Dash

share_data_callbacks.py

# See my issue at https://community.plotly.com/t/using-dcc-interval-for-continuous-update/41071/12
import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html
import logging
# from time import sleep
from tempfile import gettempdir
from os import getpid, remove
from os.path import join as pjoin, isfile
from dash.exceptions import PreventUpdate

tmpfile= pjoin(gettempdir(), f'time-{getpid()}')
if isfile(tmpfile):
    remove(tmpfile)

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
log= logging.getLogger('werkzeug')
log.setLevel(logging.ERROR)

app.layout = html.Div([
    dcc.Input(id='total', value=0, type='number'),
    html.Div(id='page-content'),
    # the layout should update every 500 mili seconds
    dcc.Interval(id= 'interval', n_intervals=0, interval=1000)
])


@app.callback(Output('page-content', 'children'),
              [Input('total', 'value'), Input('interval', 'n_intervals')])
def display_page(value, n_intervals):

    if isfile(tmpfile):
        # read value from file
        with open(tmpfile) as f:
            value = f.read()
    else:
        # value is obtained from Input
        pass


    if not value or int(value)<1:
        if isfile(tmpfile):
            remove(tmpfile)
        raise PreventUpdate

    value= int(value)
    value-= 1

    # write value back
    with open(tmpfile, 'w') as f:
        f.write(str(value))


    # return value
    return html.Div([
        html.Plaintext(f'Value: {value}')
    ])

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