Print output based on user input in dash (or shiny)

Question

I would like to get inputs x and y from a user's input to a text box.

if x + 2*y 3*x*y > 100:
    print('Blurb 1')
else:
    print('Blurb 2')

This seems to be convoluted in dash with callbacks, etc, even though it could be self-contained and quite simple. Is there a simple way to do this within a web app? Other resources I found seem to assume a much more complex goal, so I am curious as to how much the code can be pared.

Answer 1

I don't think you can accomplish your task without defining a callback, but the code to get the work done is very short and simple. A possible solution could be the following:

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

app = dash.Dash()

app.layout = html.Div([
    html.H1("Simple input example"),
    dcc.Input(
        id='input-x',
        placeholder='Insert x value',
        type='number',
        value='',
    ),
    dcc.Input(
        id='input-y',
        placeholder='Insert y value',
        type='number',
        value='',
    ),
    html.Br(),
    html.Br(),
    html.Div(id='result')
    ])


@app.callback(
    Output('result', 'children'),
    [Input('input-x', 'value'),
     Input('input-y', 'value')]
)
def update_result(x, y):
    return "The sum is: {}".format(x + y)


if __name__ == '__main__':
        app.run_server(host='0.0.0.0', debug=True, port=50800)

This is what you get:

The value of the sum is updated every time one of the two input boxes changes its values.