How do I deal with Dash (Plotly) Javascript error related to rendering of the graph?

Question

I am trying to make a dash app. I am a beginner (noob :P ) and trying app for the first time. I wrote the following code and the app runs successfully, but I am not able to get the graphs. I get the following error.

An object was provided as 'children' instead of a component, string, or number (or list of those). Check the children property that looks something like:

Here is the full error. I used pastebin to avoid spamming the post. https://pastebin.com/XiCkax0T

This is my code. I am not able to identify where I am making mistake but I think it's in the function that generates graph im_update_figure and ex_update_figure

Here is the full code.

import pandas as pd
import numpy as np

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

import plotly.graph_objects as go

ex = pd.read_csv('2018-2010_export.csv')
im = pd.read_csv('2018-2010_import.csv')

app = dash.Dash(__name__)

app.layout = html.Div([
    html.Label("Select the year"),
    dcc.Dropdown(
        id='yearInput',
        options=[
            {'label': i, 'value': i} for i in np.unique(ex.year)
        ],
        value=2010
    ),
    html.Div(id='outputGraphExport'),
    html.Div(id='outputGraphImport')
])

app.title = 'India Import Export'


@app.callback(
    Output('outputGraphImport', 'children'),
    [Input('yearInput', 'value')])
def im_update_figure(yearInput):
    df_im = im[im.year == yearInput]
    im_fig = go.Figure(
        [go.Bar(
            x=df_im.groupby('country').sum().sort_values(
                by=['value'], ascending=False).head(7).index,
            y=df_im.groupby('country').sum().sort_values(
                by=['value'], ascending=False).value.head(7),
            text=round(df_im.groupby('country').sum().sort_values(
                by=['value'], ascending=False).value.head(7)),
            textposition='auto')])
    im_fig.update_layout(
        title='Imports of India for the year 2018',
        xaxis=dict(
            title='Top 7 Countries'),
        yaxis=dict(
            title='INR (in Million)'))

    return im_fig


@app.callback(
    Output('outputGraphExport', 'children'),
    [Input('yearInput', 'value')])
def ex_update_figure(yearInput):
    df_ex = ex[ex.year == yearInput]
    ex_fig = go.Figure(
        [go.Bar(
            x=df_ex.groupby('country').sum().sort_values(
                by=['value'], ascending=False).head(7).index,
            y=df_ex.groupby('country').sum().sort_values(
                by=['value'], ascending=False).value.head(7),
            text=round(df_ex.groupby('country').sum().sort_values(
                by=['value'], ascending=False).value.head(7)),
            textposition='auto')])

    ex_fig.update_layout(
        title='Exports of India for the year 2018',
        xaxis=dict(
            title='Top 7 Countries'),
        yaxis=dict(
            title='INR (in Million)'))

    return ex_fig


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

Answer 1

Two errors

1. I was using html.Div instead of dcc.Graph which enables charting in Dash
2. I was using plotly syntax but in fact one has to use a JS enabled one.

Here is the updated code.

#the dash app for import export

import pandas as pd
import numpy as np

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

import plotly.graph_objects as go

ex = pd.read_csv('2018-2010_export.csv')
im = pd.read_csv('2018-2010_import.csv')

app = dash.Dash(__name__)

app.layout = html.Div([
    dcc.Dropdown(
        id='yearInput',
        options=[
            {'label': i, 'value': i} for i in np.unique(ex.year)
        ],
        value=2010
    ),
    dcc.Graph(id='outputGraphImport'),
    dcc.Graph(id='outputGraphExport')
])

app.title = 'India Import Export'

@app.callback(
    Output('outputGraphImport', 'figure'),
    [Input('yearInput', 'value')])
def im_update_figure(yearInput):
    df_im = im[im.year == yearInput]
    figure = {
        'data': [{
            "x":df_im.groupby('country').sum().sort_values(by=['value'], ascending=False).head(7).index,
            "y":df_im.groupby('country').sum().sort_values(by=['value'], ascending=False).value.head(7),
            "type":'bar',
        }],
        'layout':{
            'title': 'Imports to India for the selected year',
            'xaxis':{
                'title':'Countries'
            },
            'yaxis':{
                'title':'INR (Million)'
            }
        }}
    return figure


@app.callback(
    Output('outputGraphExport', 'figure'),
    [Input('yearInput', 'value')])
def ex_update_figure(yearInput):
    df_ex = ex[ex.year == yearInput]
    figure = {
        'data': [{
            "x":df_ex.groupby('country').sum().sort_values(by=['value'], ascending=False).head(7).index,
            "y":df_ex.groupby('country').sum().sort_values(by=['value'], ascending=False).value.head(7),
            "type":'bar',
        }],
        'layout':{
            'title': 'Exports from India for the selected year',
            'xaxis':{
                'title':'Countries'
            },
            'yaxis':{
                'title':'INR (Million)'
            }
        }}
    return figure

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