walmart_hovering.py

import dash
import dash_core_components as dcc
import dash_html_components as html
import plotly.graph_objs as go
import pandas as pd

app = dash.Dash()

df = pd.read_csv(
    'https://raw.githubusercontent.com/'
    'plotly/datasets/master/'
    '1962_2006_walmart_store_openings.csv')

app.layout = html.Div([
    html.H1('Walmart Store Openings'),
    html.Div(id='text-content'),
    dcc.Graph(id='map', figure={
        'data': [{
            'lat': df['LAT'],
            'lon': df['LON'],
            'marker': {
                'color': df['YEAR'],
                'size': 8,
                'opacity': 0.6
            },
            'customdata': df['storenum'],
            'type': 'scattermapbox'
        }],
        'layout': {
            'mapbox': {
                'accesstoken': 'pk.eyJ1IjoiY2hyaWRkeXAiLCJhIjoiY2ozcGI1MTZ3MDBpcTJ3cXR4b3owdDQwaCJ9.8jpMunbKjdq1anXwU5gxIw'
            },
            'hovermode': 'closest',
            'margin': {'l': 0, 'r': 0, 'b': 0, 't': 0}
        }
    })
])

@app.callback(
    dash.dependencies.Output('text-content', 'children'),
    [dash.dependencies.Input('map', 'hoverData')])
def update_text(hoverData):
    s = df[df['storenum'] == hoverData['points'][0]['customdata']]
    return html.H3(
        'The {}, {} {} opened in {}'.format(
            s.iloc[0]['STRCITY'],
            s.iloc[0]['STRSTATE'],
            s.iloc[0]['type_store'],
            s.iloc[0]['YEAR']
        )
    )

app.css.append_css({
    'external_url': 'https://codepen.io/chriddyp/pen/bWLwgP.css'
})

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

In line 44, in update_text
s = df[df['storenum'] == hoverData['points'][0]['customdata']]
TypeError: 'NoneType' object is not subscriptable

In line 44, in update_text
s = df[df['storenum'] == hoverData['points'][0]['customdata']]
TypeError: 'NoneType' object is not subscriptable

Because when initialization, the hoverData is empty. You can add default value of

html.Div(id='text-content')

In line 44, in update_text
s = df[df['storenum'] == hoverData['points'][0]['customdata']]
TypeError: 'NoneType' object is not subscriptable

Because when initialization, the hoverData is empty. You can add default value of

html.Div(id='text-content')

where i have to add default value in code i didn't get idea.

In line 44, in update_text
s = df[df['storenum'] == hoverData['points'][0]['customdata']]
TypeError: 'NoneType' object is not subscriptable

Because when initialization, the hoverData is empty. You can add default value of

html.Div(id='text-content')

where i have to add default value in code i didn't get idea.

Sorry, html.Div(id='text-content') is correct, you do not need edit it.
The input data is comes from Graph "map", in line 18. You should inspect the dcc.Graph definition from official doc, it should have an attribute 'value' or something.