Error deploying simple Dash app on Pythonanywhere

Dash Python
1

I’m trying to build a simple Dash app on Pythonanywhere but encountered errors that I don’t know how to fix. Thanks in advance!

File “app.py”:

from dash import Dash, html

dash_app = Dash()

dash_app.layout = [html.Div(children='Hello World')]

WSGI file:

import sys

# add your project directory to the sys.path
project_home = '/home/weiqizhang/mysite'
if project_home not in sys.path:
    sys.path = [project_home] + sys.path

# import flask app but need to call it "application" for WSGI to work
from app import dash_app   # noqa
application = dash_app.server

Here is the error log:
2024-06-08 04:10:49,581: Error running WSGI application
2024-06-08 04:10:49,581: dash.exceptions.NoLayoutException: Layout must be a dash component or a function that returns a dash component.
2024-06-08 04:10:49,581: File “/var/www/weiqizhang_pythonanywhere_com_wsgi.py”, line 16, in
2024-06-08 04:10:49,581: from app import dash_app # noqa
2024-06-08 04:10:49,582:
2024-06-08 04:10:49,582: File “/home/weiqizhang/mysite/app.py”, line 5, in
2024-06-08 04:10:49,582: dash_app.layout = [html.Div(children=‘Hello World’)]
2024-06-08 04:10:49,582:
2024-06-08 04:10:49,582: File “/usr/local/lib/python3.10/site-packages/dash/dash.py”, line 551, in layout
2024-06-08 04:10:49,582: _validate.validate_layout_type(value)
2024-06-08 04:10:49,582:
2024-06-08 04:10:49,582: File “/usr/local/lib/python3.10/site-packages/dash/_validate.py”, line 383, in validate_layout_type
2024-06-08 04:10:49,583: raise exceptions.NoLayoutException(
2024-06-08 04:10:49,583: ***************************************************
2024-06-08 04:10:49,583: If you’re seeing an import error and don’t know why,
2024-06-08 04:10:49,583: we have a dedicated help page to help you debug:
2024-06-08 04:10:49,583: Debugging with sys.path / ImportError issues | PythonAnywhere help
2024-06-08 04:10:49,583: ***************************************************

2

my wsgi file usually looks like:

from app import server

if __name__ == "__main__":
    server.run()

and I setup my app.py like:

from flask import Flask
from dash import *

server = Flask(__name__)

app = Dash(
    __name__)

layout= html.Div(children=['Hello World'])

# Define the main function that will run the app
if __name__ == "__main__":
    app.run_server(debug=True, host="localhost", port="8212")
3

Hi @weiqi.zhang
The wsgi file looks correct.

If you are using a virtual environment, please make sure that you are using the latest version of Dash.

As of dash 2.17 the layout can be a list of components, for example:
app.layout = [...]

Prior to dash==2.17, it was necessary for the layout to be a dash component or a function that returns a dash component. For example:
app.layout=html.Div([...])

1 Like
4

The Bash of pythonanywhere shows I’m using dash==2.4.1.

I changed the app to the following and it worked:

from dash import Dash, html

dash_app = Dash()

dash_app.layout = html.Div(html.H1("hello world"))

I’m not using virtual environment. do you think I should create one and update to dash==2.17?

5

@weiqi.zhang
Well, it depends what type of app you would like to make. You can run simple apps and most of the examples in the dash-docs using this version. You can see what’s included in the default environment here:

If you want to use the latest dash features or other libraries such as dash-bootstrap-components or dash-ag-grid, you will need to make a virtual environment.

1 Like
6

Thank you. Creating a virtualenv now.

1 Like
7

Just a few tips if you are trying to stay in the free tier:

Start by installing libraries one at a time and keep an eye on the file usage after each library. Large libraries like tensorflow will eat up all of it.

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image1162×356 28.8 KB

If you reach the limit uninstall the library and delete the cache

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image1546×744 98 KB

2 Likes