simple_app.py

# pylint: disable=missing-docstring
import dash_core_components as dcc
import dash_html_components as html
import dash
from dash.dependencies import Output, Input
from dash.exceptions import PreventUpdate


app = dash.Dash(__name__)

app.layout = html.Div(
    [
        dcc.Input(id="value", placeholder="my-value"),
        html.Div(["You entered: ", html.Span(id="out")]),
        html.Button("style-btn", id="style-btn"),
        html.Div("style-container", id="style-output"),
    ]
)


@app.callback(Output("out", "children"), Input("value", "value"))
def on_value(value):
    if value is None:
        raise PreventUpdate

    return value


@app.callback(Output("style-output", "style"), [Input("style-btn", "n_clicks")])
def on_style(value):
    if value is None:
        raise PreventUpdate

    return {"padding": "10px"}


if __name__ == "__main__":
    app.run_server(debug=True, port=10850)