Python Dash应用在回调中添加下载按钮

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import base64

app = dash.Dash(__name__)

app.layout = html.Div([
    html.Button('下载数据', id='download-button'),
    dcc.Download(id='download')
])

@app.callback(
    Output('download', 'data'),
    [Input('download-button', 'n_clicks')]
)
def download_data(n_clicks):
    if n_clicks is not None:
        # 在这里编写下载数据的逻辑
        # 将数据保存为文件，并返回文件内容
        data = "这是要下载的数据"
        data = base64.b64encode(data.encode()).decode()
        return dict(content=data, filename='data.txt')

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