上传表单 plotly-dash 应用程序时无法访问 dataframe

Question

I am new to python and plotly-dash. I am trying to use "Hidden Div" to store a data frame as suggested in dash tutorial 5. But I am not able to process the uploaded file.

    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'), [Input('intermediate-value', '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')

I am getting the following error while running the code:

File "ipython-input-12-4bd6fe1b7399", line 28, in parse_contents content_type, content_string = contents.split(',') AttributeError: 'NoneType' object has no attribute 'split'

Answer 1

The callback is likely running on initialization with empty values. You can prevent this by adding something like this at the top of your callback:

if contents is None:
   raise dash.exceptions.PreventUpdate