更新输出图时出现Plotly Dash回调错误

import dash
from dash import dcc, html
from dash.dependencies import Input, Output

app = dash.Dash(__name__)

app.layout = html.Div([
    dcc.Dropdown(
        id='dropdown',
        options=[
            {'label': 'New York City', 'value': 'NYC'},
            {'label': 'Montreal', 'value': 'MTL'},
            {'label': 'San Francisco', 'value': 'SF'}
        ],
        value='MTL'
    ),
    dcc.Graph(id='graph')
])

@app.callback(
    Output('graph', 'figure'),
    [Input('dropdown', 'value')]
)
def update_graph(selected_city):
    # 这里假设你有一个函数 get_data(selected_city) 返回相应的数据
    data = get_data(selected_city)
    figure = {
        'data': [
            {'x': data['x'], 'y': data['y'], 'type': 'bar', 'name': selected_city},
        ],
        'layout': {
            'title': f'Data for {selected_city}'
        }
    }
    return figure

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

pip install --upgrade dash plotly