Attempting to use Dash to produce intermediate output. See associated thread: https://community.plotly.com/t/returning-partial-results/46047

app.py

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State
from dash.exceptions import PreventUpdate
from datetime import datetime
import time

app = dash.Dash(__name__)

app.layout = html.Div([
    html.H6("Partial results demo"),
    html.Div(["Input: ", dcc.Input(
        id='input', 
        value='',
        placeholder='Enter a query',
        type='text')]),
    html.Br(),
    html.Div(id='output'),
    html.Div(id='intermediate', style={'display': 'none'})

])


@app.callback(
    Output(component_id='output', component_property='children'),
    [Input(component_id='input', component_property='value'), Input(component_id='intermediate', component_property='children')],
    [State(component_id='output', component_property='children')]
)
def update_output_div(input_value, intermediate_value, existing_children):
    print(dash.callback_context, datetime.now())
    if not dash.callback_context.triggered:
        raise PreventUpdate
    trigger_ids = [triggered['prop_id'].split('.')[0] for triggered in dash.callback_context.triggered]
    trigger_str = str(dash.callback_context.triggered)
    
    if existing_children is None:
        existing_children = ['Output:', html.Br()]
    
    new_children = []
    
    if 'input' in trigger_ids:
        # fast computation, return immediately
        new_children.extend([f"Fast result at {datetime.now()} (trigger: {trigger_str})", html.Br()])
    if 'intermediate' in trigger_ids:
        # the slow computation finished! add it to the output
        new_children.extend([intermediate_value, f"(trigger: {trigger_str})", html.Br()])
    return existing_children + new_children

@app.callback(
    Output('intermediate', 'children'),
    Input('input', 'value')
)
def update_intermediate_div(input_value):
    if input_value.strip() == '':
        raise PreventUpdate
    s = datetime.now()
    time.sleep(5)
    long_running_result = f"Slow result at {datetime.now()} after {datetime.now() - s} "
    return long_running_result

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