在Dash的下拉列表中添加"select-all“选项

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

app = dash.Dash(__name__)

app.layout = html.Div([
    dcc.Dropdown(
        id='dropdown',
        options=[
            {'label': 'Option 1', 'value': 'option1'},
            {'label': 'Option 2', 'value': 'option2'},
            {'label': 'Option 3', 'value': 'option3'},
            {'label': 'select-all', 'value': 'select-all'}
        ],
        value=[],
        multi=True
    ),
    html.Div(id='output')
])

@app.callback(
    Output('dropdown', 'value'),
    Input('dropdown', 'value')
)
def update_dropdown(value):
    if 'select-all' in value:
        return ['option1', 'option2', 'option3']
    elif len(value) == 3:
        return ['select-all']
    else:
        return value

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