How to add callbacks for multiple graphs in a Dash/Plotly app automatically

Question

In a single-page Dash by Plotly app I want to show many similar graphs.

For this I have created a "factory class" which can generate many graphs.

This class exposes methods to be used in the Dash app's app.layout and @app.callback code. A sample app.py with two graphs looks like this:

import ...

app = dash.Dash(__name__)

graph_A = GraphFactory(feature="A")
graph_B = GraphFactory(feature="B")

app.layout = html.Div([
            graph_A.graph(),
            graph_B.graph(),
            ])

@app.callback(
    graph_A.callback_output(), graph_A.callback_inputs()
)
def update_A(value):
    return graph_A.callback_update(value)

@app.callback(
    graph_B.callback_output(), graph_B.callback_inputs()
)
def update_B(value):
    return graph_B.callback_update(value)

This works fine. However I want to display many graphs from a list of GraphFactory objects. It's easy to create the objects and put them in the app layout:

graph_list = [ GraphFactory(feature=f) for f in feature_list ]

app.layout = html.Div([ 
            g.graph() for g in graph_list
            ])

But **how can I add the many callback_output(), callback_inputs() and callback_update(value) calls? Is there a way to write the decorator and the function only once and add the calls to the callback_... functions in there?

Answer 1

By digging into decorators I found a solution myself: You can call the Dash decorator on the object's callback_update function directly. So for the example from the question you can write:

for g in graph_list:
    dash_app.callback(g.callback_output(),
                      g.callback_inputs())(g.callback_update)

Please note carefully, that g.callback_update has no (), because the app.callback function is applied to the g.callback_update function/method, not as usual to its return value.