bug in pattern-matching background callbacks #3169

dash                 2.18.2

import dash
from dash import dcc, html, Input, Output, ctx, MATCH, DiskcacheManager, no_update
import time

import diskcache
cache = diskcache.Cache("./cache")

background_callback_manager = DiskcacheManager(cache)

# Initialize the Dash app
app = dash.Dash(__name__, background_callback_manager=background_callback_manager)

# Define the layout of the app
app.layout = html.Div([
    html.Div(id='progress-container', children=[
        *[html.Div(id={'type': 'progress', 'index': i}, children=f'{i}') for i in range(3)],
        *[html.Button(id={'type': 'button', 'index': i}, children=f'trigger-{i}') for i in range(3)]
    ]),
    html.Div(id='test-out'),
    html.Button(id='download_test', children='Download Test'),
    dcc.Download(id='download_file')
])

# Pattern-matching callback to update progress
@app.callback(
    Output({'type': 'progress', 'index': MATCH}, 'children'),
    Input({'type': 'button', 'index': MATCH}, 'n_clicks'),
    progress=[Output('test-out', 'children')],
    background=True,
    prevent_initial_call=True
)
def update_progress(set_progress, n):
    if n:
        count = 0
        while count < 100:
            count += 10
            set_progress(f'{ctx.triggered_id.index} - {count}')
            time.sleep(1)
        # Read the existing data from the file
        try:
            with open('test.txt', 'r') as f:
                data = f.readlines()
        except:
            data = []

        # Append the new line to the data
        data.append(f'{ctx.triggered_id.index} - {n}\n')

        # Write the updated data back to the file
        with open('test.txt', 'w') as f:
            f.writelines(data)
        return 'Task Complete!'
    return no_update

@app.callback(
    Output('download_file', 'data'),
    Input('download_test', 'n_clicks'),
    prevent_initial_call=True
)
def downfile(n):
    if n:
        with open('test.txt', 'r') as f:
            data = f.read()  # Read the entire file content
        return dcc.send_bytes(data.encode(), filename='test.txt')
    return no_update


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