Grouped bar chart doesn't work in Django dash

Dash Python
1 
import dash
from django_plotly_dash import DjangoDash
import dash_core_components as dcc
import dash_html_components as html
import plotly.express as px
import pandas as pd

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = DjangoDash('app1', external_stylesheets=external_stylesheets)

# assume you have a "wide-form" data frame with no index
# see https://plotly.com/python/wide-form/ for more options
df = pd.DataFrame({"x": [1, 2, 3], "SF": [4, 1, 2], "Montreal": [2, 4, 5]})

fig = px.bar(df, x="x", y=["SF", "Montreal"], barmode="group")

app.layout = html.Div(children=[
    html.H1(children='Hello Dash'),

    html.Div(children='''
        Dash: A web application framework for Python.
    '''),

    dcc.Graph(
        id='example-graph',
        figure=fig
    )
])

This is my code and instead of dash,I used djangodash.It shows an error