Error when running app (Flask)

Dash Python
1

When running an app, I keep coming across the error message, “can not import name app from app.” Please advise or provide resources.

2

You have sample code you can share that causes this error? hard to provide advise or duplicate w/o it.

3

Please post sample code - but it’s likely you have a circular reference somewhere in your code. To avoid any issues like this, I always use separate app (app and callbacks), server (flask instance if necessary for login etc.), and index (run the actual app) files if the project is not a single file app.

4

I was trying to run this sample code plotly provided so that I can replicate something similar to this, but I came across this error.

import os

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

from app import app

df = pd.read_csv(
‘https://gist.githubusercontent.com/chriddyp/’
‘c78bf172206ce24f77d6363a2d754b59/raw/’
‘c353e8ef842413cae56ae3920b8fd78468aa4cb2/’
‘usa-agricultural-exports-2011.csv’)

if ‘DYNO’ in os.environ:
app_name = os.environ[‘DASH_APP_NAME’]
else:
app_name = ‘dash-barplot’

layout = html.Div([
html.H1(“Food Product Exports in the United States”, style={“textAlign”: “center”}),
html.Div([html.Div([dcc.Dropdown(id=‘product-selected1’,
options=[{‘label’: i.title(), ‘value’: i} for i in df.columns.values[2:]],
value=“poultry”)], className=“six columns”,
style={“width”: “40%”, “float”: “right”}),
html.Div([dcc.Dropdown(id=‘product-selected2’,
options=[{‘label’: i.title(), ‘value’: i} for i in df.columns.values[2:]],
value=‘beef’)], className=“six columns”, style={“width”: “40%”, “float”: “left”}),
], className=“row”, style={“padding”: 50, “width”: “60%”, “margin-left”: “auto”, “margin-right”: “auto”}),
dcc.Graph(id=‘my-graph’),

# dcc.Link('Go to Source Code', href='{}/code'.format(app_name))

], className=“container”)

@app.callback(
dash.dependencies.Output(‘my-graph’, ‘figure’),
[dash.dependencies.Input(‘product-selected1’, ‘value’),
dash.dependencies.Input(‘product-selected2’, ‘value’)])
def update_graph(selected_product1, selected_product2):
dff = df[(df[selected_product1] >= 2) & (df[selected_product2] >= 2)]
trace1 = go.Bar(x=dff[‘state’], y=dff[selected_product1], name=selected_product1.title(), )
trace2 = go.Bar(x=dff[‘state’], y=dff[selected_product2], name=selected_product2.title(), )

return {
    'data': [trace1, trace2],
    'layout': go.Layout(title=f'State vs Export: {selected_product1.title()}, {selected_product2.title()}',
                        colorway=["#EF963B", "#EF533B"], hovermode="closest",
                        xaxis={'title': "State", 'titlefont': {'color': 'black', 'size': 14},
                               'tickfont': {'size': 9, 'color': 'black'}},
                        yaxis={'title': "Export price (million USD)", 'titlefont': {'color': 'black', 'size': 14, },
                               'tickfont': {'color': 'black'}})}

ImportError: cannot import name ‘app’ from 'app

5

Here is the corrected code. If you got the code from their website, it may not have been updated. This works for me running dash v. 1.2.0.

I changed the app definition at the top, added the app.run_sever if-statement at the bottom.

import os

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

app = dash.Dash(__name__)

df = pd.read_csv('https://gist.githubusercontent.com/chriddyp/' +
                 'c78bf172206ce24f77d6363a2d754b59/raw/' +
                 'c353e8ef842413cae56ae3920b8fd78468aa4cb2/' +
                 'usa-agricultural-exports-2011.csv')

if 'DYNO' in os.environ:
    app.title = os.environ['DASH_APP_NAME']
else:
    app.title = 'dash-barplot'

app.layout = html.Div([
    html.H1('Food Product Exports in the United States', style={'textAlign': 'center'}),
    html.Div([html.Div([dcc.Dropdown(id='product-selected1',
                                     options=[{'label': i.title(), 'value': i}
                                              for i in df.columns.values[2:]],
                                     value='poultry')], className='six columns',
                       style={'width': '40 %', 'float': 'right'}),
              html.Div([dcc.Dropdown(id='product-selected2',
                                     options=[{'label': i.title(), 'value': i}
                                              for i in df.columns.values[2:]],
                                     value='beef')], className='six columns', style={'width': '40 %', 'float': 'left'}),
              ], className='row', style={'padding': 50, 'width': '60 %', 'margin-left': 'auto', 'margin-right': 'auto'}),
    dcc.Graph(id='my-graph'),

    # dcc.Link('Go to Source Code', href='{}/code'.format(app_name))
    ], className='container')


@app.callback(
    dash.dependencies.Output('my-graph', 'figure'),
    [dash.dependencies.Input('product-selected1', 'value'),
     dash.dependencies.Input('product-selected2', 'value')])
def update_graph(selected_product1, selected_product2):
    dff = df[(df[selected_product1] >= 2) & (df[selected_product2] >= 2)]


    trace1 = go.Bar(x=dff['state'], y=dff[selected_product1],
                name=selected_product1.title(), )
    trace2 = go.Bar(x=dff['state'], y=dff[selected_product2],
                name=selected_product2.title(), )

    return {
        'data': [trace1, trace2],
        'layout': go.Layout(title=f'State vs Export: {selected_product1.title()}, {selected_product2.title()}',
                            colorway=['#EF963B', '#EF533B'], hovermode='closest',
                            xaxis={'title': 'State', 'titlefont': {'color': 'black', 'size': 14},
                                   'tickfont': {'size': 9, 'color': 'black'}},
                            yaxis={'title': 'Export price (million USD)', 'titlefont': {'color': 'black', 'size': 14, },
                                   'tickfont': {'color': 'black'}})}

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