Receiving "error loading dependencies" message; actual problem is unclear

[jwhendy]

Here is a minimal example after doing some trial and error to pin it down:

#!/usr/bin/env python2
# -*- coding: utf-8 -*-

import dash
import dash_core_components as dcc
import dash_html_components as html


def generate_inputs():

    in_a_lab = html.Label('input a')
    in_a = dcc.Input(type='number',
                      value=1)
    
    in_b = [html.Label(html.Strong('input b')),
            dcc.Input(type='number', value=1)]

    inputs = [in_a_lab, in_a]

    # uncomment this line to cause error
    # inputs = [in_a_lab, in_a, in_b]

    return inputs

app = dash.Dash()
app.layout = html.Div([
    # switch the comment on these lines to cause an error
    html.Div(generate_inputs())
    # generate_inputs()
]) # app.layout


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

I started on the path of python3, but ran into some dependency hell on Ubuntu 16.04, so I reinstalled with python2. This created what I believe to be some actual dependency issues around urllib3 and chardet. I was getting dependency warnings about the wrong versions on the command line when I would do python2 app.py.

With those solved, the command line looked fine, but I'd get this in the browser:

I was in the process of building some ui elements and doing them in pairs, with a label and then matching input. Then I wanted to switch to a list of the label and pair together. I realized I was sending back a nested list (the above would generated something like [in_a_lab, in_a, [in_b_lab, in_b]]). So, that was a definite issue, but I wouldn't expect the result to be error loading dependencies.

On accident I found that without wrapping the function return in html.Div() I'm also getting the same error.

This is probably an issue on my part with something I don't understand about dash (totally likely; I'm all of 2-3 hours into playing with it). That said, if this is isn't really a "dependency error," might there be room improving the error message? From what I'm seeing, this strikes me as more of a syntax error, or something like "expected blah object, got blah instead"?

Thanks for taking a look.

[chriddyp]

Yeah, this is a really bad error message. In fact, dependencies in this case doesn't even refer to the python dependencies, it refers to an underling /_dash-dependencies API endpoint... 🤕

[jasper-muller]

Got the same issue here. Installed dash using

pip install dash
pip install dash-renderer
pip install dash-html-components
pip install dash-core-components
pip install plotly --upgrade

Next, I followed the scatterplot example in the getting started guide: https://plot.ly/dash/getting-started

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

app = dash.Dash()

df = pd.read_csv(
    'https://gist.githubusercontent.com/chriddyp/' +
    '5d1ea79569ed194d432e56108a04d188/raw/' +
    'a9f9e8076b837d541398e999dcbac2b2826a81f8/'+
    'gdp-life-exp-2007.csv')


app.layout = html.Div([
    dcc.Graph(
        id='life-exp-vs-gdp',
        figure={
            'data': [
                go.Scatter(
                    x=df[df['continent'] == i]['gdp per capita'],
                    y=df[df['continent'] == i]['life expectancy'],
                    text=df[df['continent'] == i]['country'],
                    mode='markers',
                    opacity=0.7,
                    marker={
                        'size': 15,
                        'line': {'width': 0.5, 'color': 'white'}
                    },
                    name=i
                ) for i in df.continent.unique()
            ],
            'layout': go.Layout(
                xaxis={'type': 'log', 'title': 'GDP Per Capita'},
                yaxis={'title': 'Life Expectancy'},
                margin={'l': 40, 'b': 40, 't': 10, 'r': 10},
                legend={'x': 0, 'y': 1},
                hovermode='closest'
            )
        }
    )
])

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

Which results in the following output in my terminal:

 * Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)
127.0.0.1 - - [22/Sep/2017 16:42:18] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [22/Sep/2017 16:42:18] "GET /_dash-layout HTTP/1.1" 200 -
127.0.0.1 - - [22/Sep/2017 16:42:18] "GET /_dash-dependencies HTTP/1.1" 200 -

And in my browser:

I'm running this from a virtual environment with the following packages installed:

alabaster==0.7.10
appnope==0.1.0
astroid==1.5.3
Babel==2.3.4
bleach==1.5.0
bumpversion==0.5.3
certifi==2017.7.27.1
chardet==3.0.4
click==6.7
cycler==0.10.0
dash==0.18.3
dash-core-components==0.12.6
dash-html-components==0.7.0
dash-renderer==0.10.0
decorator==4.1.2
docutils==0.13.1
eneco==1.0.0
entrypoints==0.2.3
et-xmlfile==1.0.1
Flask==0.12.2
Flask-Compress==1.4.0
Flask-SeaSurf==0.2.2
hmmlearn==0.2.0
html5lib==0.9999999
idna==2.6
imagesize==0.7.1
ipykernel==4.6.1
ipython==6.1.0
ipython-genutils==0.2.0
isort==4.2.9
itsdangerous==0.24
jdcal==1.3
jedi==0.10.2
Jinja2==2.9.6
jsonschema==2.6.0
jupyter-client==5.1.0
jupyter-core==4.3.0
lazy-object-proxy==1.3.0
line-profiler==2.0
MarkupSafe==1.0
matplotlib==2.0.2
mccabe==0.6.1
mistune==0.7.4
nb-conda==2.2.0
nb-conda-kernels==2.1.0
nbconvert==5.2.1
nbformat==4.4.0
notebook==5.0.0
numpy==1.12.1
numpydoc==0.7.0
openpyxl==2.4.8
pandas==0.20.1
pandocfilters==1.4.1
patsy==0.4.1
pep8==1.7.0
pexpect==4.2.1
pickleshare==0.7.3
plotly==2.0.15
prompt-toolkit==1.0.14
psutil==5.2.1
ptyprocess==0.5.2
pyflakes==1.5.0
Pygments==2.2.0
pylint==1.7.1
pyparsing==2.2.0
python-dateutil==2.6.1
python-dotenv==0.6.4
pytz==2017.2
pyzmq==16.0.2
QtAwesome==0.4.4
qtconsole==4.3.0
QtPy==1.2.1
requests==2.18.4
rope==0.10.5
scikit-learn==0.18.2
scipy==0.19.0
seaborn==0.7.1
simplegeneric==0.8.1
six==1.11.0
snowballstemmer==1.2.1
Sphinx==1.6.3
sphinxcontrib-websupport==1.0.1
spyder==3.1.4
statsmodels==0.8.0
terminado==0.6
testpath==0.3
tornado==4.5.1
tqdm==4.17.0
traitlets==4.3.2
typing==3.6.1
urllib3==1.22
wcwidth==0.1.7
webencodings==0.5
Werkzeug==0.12.2
wrapt==1.10.8
xlrd==1.0.0
XlsxWriter==0.9.8

[jasper-muller]

I'm embarrassed to say that it turned out to be my ad blocker that was causing the problem.

Disabling ad block solved my issue.

[abieler]

I do get the same error every once in a while. It is not reproducible in my case as it suddenly starts/stops working without changing the code or anything. I first thought it is a browser problem as it initially happened only on Firefox and Chrome was fine. Happens on Chrome now too.

[jwhendy]

@abieler and @jasper-muller did you try my example above? I'm curious if it reproduces for either of you, or if it's possibly an ad blocker (which I also use) or sporadic/browser related.

In my experience, it was reproducible by toggling the called out comment lines.

[jmineraud]

I have been running into the same issue while trying to follow the tutorial at . I am using virtualenv with Python 3 and I have install only the libraries required by Dash. I have tried to run from the same environment the example from and it works fine. So I believe, when I run python usage.py that the error loading dependencies message occurs when loading my example component (straight from the archetype, v0.2.11). Is there a way to do a quick fix that would enable me to load my custom component dependency ?

[jmineraud]

I would like to add that npm run demo seems to work fine

[jasper-muller]

@jwhendy tried your example and get the same error as you are getting: Error loading dependencies.

[abieler]

@jwhendy the issue is how you stack your input lists.
Doing

    inputs = [in_a_lab, in_a]
    inputs.extend(in_b)

works for me.
In your solution inputs is a nested list, where with this one here it is a plain list.
That said, the error message is not ideal.

[jwhendy]

@abieler Agreed. Note this from my original post:

I realized I was sending back a nested list (the above would generated something like [in_a_lab, in_a, [in_b_lab, in_b]]). So, that was a definite issue, but I wouldn't expect the result to be error loading dependencies.

and

That said, if this is isn't really a "dependency error," might there be room improving the error message?

This issue is about what I see as some sort of "blanket" error message that isn't accurate or very helpful in debugging. So, yes, I passed a nested list. "Error loading dependencies" had very little chance in helping me find that out (being new).

I brought this issue forward so that the developers who know the internals of dash might be able to send back a message that more accurately describes what's wrong.

[abieler]

lol thats what I get for not reading through the whole post :)

[jwhendy]

@abieler It's all good, and I actually forgot why I wanted you to replicate... I was noting that @jasper-muller found the issue related to adblock, and you said it was sporadic. I just wanted to make sure this wasn't on my end, as I wasn't experiencing it as sporadic. Thanks!

[astratis]

Not an optimal solution but worked for me after installing again dash, hope it helps.

[tuckergordon]

Wanted to follow-up that I think I'm having an issue similar to @jmineraud in that I'm trying to follow this tutorial to create a custom component and run it within a multi-page app. Unfortunately, I'm getting the "Error loading dependencies" message. I've made sure to include the component in app.layout to ensure that Dash sees it when looking for depencies and to avoid the known issue.

Any ideas as to what could be going wrong?