Plotly express bar chart yields server error

Dash Python
1

In a dash callback I load a simple dataframe in a ploty express bar chart.
In dataframe df I have columns ‘hour’ and ‘count’. I have 7 rows.
When using:
fig = px.bar(df, x=‘hour’, y=‘count’) I get a server error. Not always though.
Anyone knows what this could be?
With a standard fig I do not get the error.

’

2

Hey @Bastituta,
Can you show us the traceback of code? and please show the full code so that we can see what you are doing and what you are expecting?

3

Thanks for helping me!
It is quite a lot of code. I took out the relevant parts.
I do not know how to figure out what the problem is.
Just before px.bar I am able to print things, so that works okay.
Actually, px.bar sometimes loads, but oftne doesn’t.
Sorry for the bad appearance, I do not know how to save code as markdown (I am not a programmer).

Here is part of the code:

necessary input

import dash
import dash_core_components as dcc
from dash.dependencies import Input, Output, State, ALL
import dash_html_components as html
from dash.exceptions import PreventUpdate
from app import app
import dash_leaflet as dl
import plotly.express as px
import pandas as pd
import spatialite

part of the layout

    html.Div([
        dl.Map([dl.TileLayer(url=Stadia_AlidadeSmoothDark), dl.Pane([dl.LayerGroup(id="container3", children=[])], style ={"z-index": 203}),
        dl.Pane([dl.LayerGroup(id="container2", children=[])], style ={"z-index": 202}),
        dl.Pane([dl.LayerGroup(id="container1", children=[])], style ={"z-index": 201})],
        id="map", bounds=image_bounds, style={'width': '90%', 'height': '80vh', 'margin-top': "20px", "display": "block"}),

the relevant callback

@app.callback([Output(“container3”, “children”),Output(“grafiek”, “figure”),Output(“totaal”, “children”)],[Input({‘type’: ‘basismarkers’, ‘index’: ALL}, ‘n_clicks’)])
def select_marker(*args):

selmarkers = []
triggered = dash.callback_context.triggered

if len(triggered) > 1 or (len(triggered) == 1 and triggered[0]['value'] == 0):
    raise PreventUpdate

conn = spatialite.connect(sqlitepath)

marker_id = triggered[0]["prop_id"].split(":")[1][1:7]
df0 =pd.read_sql('''SELECT latitude, longitude from herkomsten_REF_O where PC6 = "''' + marker_id + '''"''', conn)
lat = df0.iloc[0]['latitude']
lon = df0.iloc[0]['longitude']

selmarker = dl.Marker(children=dl.Tooltip(marker_id),position=[lat,lon],icon=icon_selected,
   id="marker2" + marker_id)
selmarkers.append(selmarker)

df1 = pd.read_sql('''select * from HBs_REF_O where PC6 ="''' + marker_id + '''"''', conn)

for index, row in df1.iterrows():
    marker = dl.Marker(children=dl.Tooltip(row["PC6_2"]),position=[row["latitude"], row["longitude"]],icon=icon_destinations,
       id="marker2" + row['PC6_2'])
    selmarkers.append(marker)

df = pd.read_sql('''select * from tijden_REF_O where PC6 ="''' + marker_id + '''"''', conn)


try:
    totaal = df.groupby(['PC6'])['count'].sum().iloc[0]
    tot = 'Totaal voor ' + marker_id + ': {}'.format(totaal)
except:
    tot =''

# from here it goes sometimes wrong
fig = px.bar(df0, x='uur', y='count', color = 'typerit', title= 'Aankomsten en vertrekken', range_x=[0,23],
             labels={"count": "ritten" }, hover_data=['count'], barmode = 'stack')

del df0, df1, df

conn.close()
return selmarkers, fig, tot

The relevant dataframe looks like this:
df = pd.read_sql(’’‘select * from tijden_REF_O where PC6 ="’’’ + marker_id + ‘’’"’’’, conn)

index     PC6  uur  count   typerit

0 647 7382SB 13 1 vertrek
1 648 7382SB 14 14 vertrek
2 649 7382SB 15 4 vertrek
3 650 7382SB 16 26 vertrek
4 651 7382SB 17 17 vertrek
5 1492 7382SB 7 1 aankomst
6 1493 7382SB 8 1 aankomst
7 1494 7382SB 9 48 aankomst

4

I was asking for error you get.

5

Thanks!
I do not know how to find the error. Don’t know how to open the browser’s console.
I get the following message:
image.png