上载表单Plotly-dash应用程序时无法访问数据框

如何解决上载表单Plotly-dash应用程序时无法访问数据框

我是python和plotly-dash的新手。 我正在尝试使用“隐藏Div”来存储仪表板教程5中建议的数据框。 但是我无法处理上传的文件。

    import base64
    import io
    import dash
    from dash.dependencies import Input,Output,State
    import dash_core_components as dcc
    import dash_html_components as html
    import dash_table
    import pandas as pd


    #global_df = pd.read_csv('...')

    app = dash.Dash(__name__)

    app.layout = html.Div([
                            dcc.Graph(id='graph'),html.Table(id='table'),dcc.Upload(
                                        id='datatable-upload',children=html.Div(['Drag and Drop or ',html.A('Select Files')]),),# Hidden div inside the app that stores the intermediate value
                            html.Div(id='intermediate-value',style={'display': 'none'})
                            ])

    def parse_contents(contents,filename):
        content_type,content_string = contents.split(',') #line 28
        decoded = base64.b64decode(content_string)
        if 'csv' in filename:
            # Assume that the user uploaded a CSV file
            return pd.read_csv(
                io.StringIO(decoded.decode('utf-8')))
        elif 'xls' in filename:
            # Assume that the user uploaded an excel file
            return pd.read_excel(io.BytesIO(decoded))
        elif 'xlsx' in filename:
            # Assume that the user uploaded an excel file
            return pd.read_excel(io.BytesIO(decoded))


    @app.callback(Output('intermediate-value','children'),[Input('datatable-upload','contents')],[State('datatable-upload','filename')])
    def update_output(contents,filename):
         # some expensive clean data step
        cleaned_df = parse_contents(contents,filename)

         # more generally,this line would be
         # json.dumps(cleaned_df)
        return cleaned_df.to_json(date_format='iso',orient='split')

    @app.callback(Output('graph','figure'),[Input('intermediate-value','children')])
    def update_graph(jsonified_cleaned_data):

        # more generally,this line would be
        # json.loads(jsonified_cleaned_data)
        dff = pd.read_json(jsonified_cleaned_data,orient='split')

        figure = create_figure(dff)
        return figure

    @app.callback(Output('table','children')])
    def update_table(jsonified_cleaned_data):
        dff = pd.read_json(jsonified_cleaned_data,orient='split')
        table = create_table(dff)
        return table

    if __name__ == '__main__':
        app.run_server(port=8050,host='0.0.0.0')

运行代码时出现以下错误：

文件“ ipython-input-12-4bd6fe1b7399”，第28行，位于parse_contents中 content_type，content_string = contents.split（'，'） AttributeError：'NoneType'对象没有属性'split'

解决方法

该回调可能在具有空值的初始化上运行。您可以通过在回调的顶部添加如下内容来防止这种情况：

if contents is None:
   raise dash.exceptions.PreventUpdate