dashboard - Python Dash TypeError: cannot convert 'NoneType' object to bytes

Question

I am trying to build a dashboard using Dash. I keep getting this error when I go to the default website http://127.0.0.1:8050/ and I get TypeError: cannot convert 'NoneType' object. Check the image for the error. My code does not have any mistakes and I was able to run it before and the dashboard would work perfectly. Can someone please help me? Here is the code:

import dash  # (version 1.12.0) pip install dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import datetime
from datetime import date


app = dash.Dash(__name__)

# App layout
app.layout = html.Div([

    html.H1("Snodas SWE/SD For January", style={'text-align': 'center'}),

    
    dcc.DatePickerSingle(
        id='my-date-picker-single',
        min_date_allowed=date(2020, 1, 1),
        max_date_allowed=date(2020, 12, 30),
        initial_visible_month=date(2020, 1, 1),
        date=date(2020, 1, 1)
    ),
    
    html.Div(id='output-container-date-picker-single'),
    
    dcc.Checklist(
    options=[
        {'label': 'SWE', 'value': 'SWE'},
        {'label': 'SD', 'value': 'SD'}
    ],
    labelStyle={'display': 'inline-block'}
    ),

    html.Iframe(id='map', srcDoc=open('map1.html', 'r').read(), width='100%', height='1000')

])

@app.callback(
    Output('map', 'srcDoc'),
    Input('my-date-picker-single', 'date'))
def update_output(date):
    return open('map_swe_sd_{}.html'.format(str(date)), 'r').read()

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

Error Message

question from:https://stackoverflow.com/questions/66054086/python-dash-typeerror-cannot-convert-nonetype-object-to-bytes

Answer 1

Try this:

@app.callback(
    Output('map', 'srcDoc'),
    Input('my-date-picker-single', 'date'))
def update_output(date):
    if not date:
        raise dash.exceptions.PreventUpdate
    return open('map_swe_sd_{}.html'.format(str(date)), 'r').read()