Expected type: (<class 'tuple'>, <class 'list'>) Received value of type <class 'NoneType'>: None

Dash Python
1

I am getting a callback error

Schema: [<Output `output_filetype.children`>, <Output `output-data-upload.children`>]
Path: ()
Expected type: (<class 'tuple'>, <class 'list'>)
Received value of type <class 'NoneType'>:
    None

I think the problem is in return of update_output() function.

import chart_studio as py
import plotly.graph_objs as go
from plotly.offline import download_plotlyjs, init_notebook_mode, plot, iplot
import pandas as pd
import json
import xlrd
import openpyxl
import dash
from dash import Dash, dcc, html, Input, Output, dash_table
from dash.dependencies import State
import plotly.express as px
import plotly.io as pio
import base64
import datetime
from dash import no_update
import io

pio.renderers.default = "browser"
external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)

app.layout = html.Div([
    dcc.Dropdown(['Excel Sheet', 'CSV File'], id='file_type', multi=False, style={'width': "40%"}),
    html.Div(id='output_filetype', children=[]),

    dcc.Upload(
        id='upload-data',
        children=html.Div([
            'Drag and Drop or ',
            html.A('Select Files')
        ]),
        style={
            'width': '100%',
            'height': '60px',
            'lineHeight': '60px',
            'borderWidth': '1px',
            'borderStyle': 'dashed',
            'borderRadius': '5px',
            'textAlign': 'center',
            'margin': '10px'
        },
        # Allow multiple files to be uploaded
        multiple=False
    ),
    html.Div(id='output-data-upload'),


])

def parse_contents(contents, filename, date):
    content_type, content_string = contents.split(',')

    decoded = base64.b64decode(content_string)
    try:
        if 'csv' in filename:
            # Assume that the user uploaded a CSV file
            df = pd.read_csv(
                io.StringIO(decoded.decode('utf-8')))
        elif 'xls' in filename:
            # Assume that the user uploaded an excel file
            df = pd.read_excel(io.BytesIO(decoded))
    except Exception as e:
        print(e)
        return html.Div([
            'There was an error processing this file.'
        ])

    return html.Div([
        html.H5(filename),
        html.H6(datetime.datetime.fromtimestamp(date)),

        dash_table.DataTable(
            df.to_dict('records'),
            [{'name': i, 'id': i} for i in df.columns]
        ),

        html.Hr(),  # horizontal line

        # For debugging, display the raw contents provided by the web browser
        html.Div('Raw Content'),
        html.Pre(contents[0:200] + '...', style={
            'whiteSpace': 'pre-wrap',
            'wordBreak': 'break-all'
        })
    ])

@app.callback(
    [Output('output_filetype', 'children'),
    Output('output-data-upload', 'children')],
    [Input(component_id='file_type', component_property='value'),
    Input('upload-data', 'contents')],
    [State('upload-data', 'filename'),
    State('upload-data', 'last_modified')],
)

def update_output(value, contents, names,  dates):
    container = "{}".format(value)
    if contents is not None:
        children = [
            parse_contents(c, n, d) for c, n, d in
            zip(contents, names, dates)]
        return container, children


if __name__ == '__main__':
    app.run_server(debug=True)
2

Hello friend,
change these two lines and see the results:
from dash import Dash, dcc, html, dash_table
from dash.dependencies import State, , Input, Output

3

Hello.
I changed the import lines but still the same error.