How to fix ImportError: cannot import name 'Event' in Dash from plotly (python)?

Question

i am working on data visualization task in which used Dash from plotly(python). when i am running the code i got an error which is -

ImportError: cannot import name 'Event'

i have tried various installation processes like pip install events or pip install Event , but i am not able to get my error's solution.

code:

import dash
from dash.dependencies import Output, Event
import dash_core_components as dcc
import dash_html_components as html
import plotly
import random
import plotly.graph_objs as go  
from collections import deque

x = deque(maxlen=20)
y = deque(maxlen=20)

x.append(1)
y.append(1)

app = dash.Dash(__name__)

app.layout = html.Div(
    [ 
        dcc.Graph(id = 'live-graph', animate = True),
        dcc.Interval(
                id = 'graph-update',
                    interval = 1000
                )

        ]
    )   

@app.callback(Output('live-graph','figure'),
                events = [Event('graph-update','interval')])

def update_graph():

    globalx
    globaly

    x.append(x[-1]+1)
    y.append(y[-1]+(y[-1]*random.uniform(-0.1,0.1)))

    data = go.Scatter(

            x = list (x),
            y = list(y),
            name = 'Scatter',
            mode = 'lines+markers'      
        )   

    return {'data':[data],'layout':go.Layout(xaxis = dict(range = [min(x), max(x)]),
                                yaxis = dict(range = [min(y), max(y)]))}                                                        


if __name__ == '__main__':
    app.run_server(debug = True, port = 8051) 

Answer 1

Event was removed in the latest version (0.37) of Dash, that's why you cannot import it. See dev comment .

If you're bent on using it, switch to 0.36, but I'd not recommend that.

Answer 2

To preserve using the latest Dash version and keep updated you can use following code to fix the problem:

import dash
from dash.dependencies import Output, Input
import dash_core_components as dcc
import dash_html_components as html
import plotly
import random
import plotly.graph_objs as go
from collections import deque

X = deque(maxlen=20)
X.append(1)
Y = deque(maxlen=20)
Y.append(1)


app = dash.Dash(__name__)
app.layout = html.Div(
    [
        dcc.Graph(id='live-graph', animate=True),
        dcc.Interval(
            id='graph-update',
            interval=1*1000
        ),
    ]
)

@app.callback(Output('live-graph', 'figure'),
              [Input('graph-update', 'n_intervals')])
def update_graph_scatter(input_data):
    X.append(X[-1]+1)
    Y.append(Y[-1]+Y[-1]*random.uniform(-0.1,0.1))

    data = plotly.graph_objs.Scatter(
            x=list(X),
            y=list(Y),
            name='Scatter',
            mode= 'lines+markers'
            )

    return {'data': [data],'layout' : go.Layout(xaxis=dict(range=[min(X),max(X)]),
                                                yaxis=dict(range=[min(Y),max(Y)]),)}


if __name__ == '__main__':
    app.run_server(host='0.0.0.0', port=8080 ,debug=True)

The change in this code is just in the callback. The word n_intervals is the new way of Dash to handle events. As the name suggests, n_intervals keeps count of how many times the interval has fired, and so each time the interval fires, n_intervals gets incremented which triggers your callback. The only change you have to make to the callback is to an argument to receive n_intervals, which you can then ignore in the function body.