Dash Error using Multiple Output

Dash Python
1

I am trying to create dash table on Web using Inputs. However the issue is that the data is created from database from the callback and a priori, I do not know the names of the columns unless the pandas dataframeis created using the callback function.
I have checked that I getting correct data. However not able to display it. I have used multiple output options (using Dash 0.41)

My code looks as follows: ( I have not provided the details of the function which generates the pandas dataframe in the callback someFunc, as that was not important for the purpose of this Dash code TroubleShooting.

import dash_table as dt

def someFunc(ID, pattern_desc, file_path):

## do something

return df # pandas dataframe
######################################################################
external_stylesheets = [‘https://codepen.io/chriddyp/pen/bWLwgP.css’]

app = dash.Dash(name, external_stylesheets=external_stylesheets)

server = app.server

app = dash.Dash(name)

app.config.suppress_callback_exceptions = True
app.css.config.serve_locally = True
app.scripts.config.serve_locally = True

app.layout = html.Div(
children = [
html.Div(
id = ‘title’,
children = appTitle,
className = ‘titleDiv’
),
html.Div(
children = [
html.Div(
children = “Enter ID:”,
className = ‘textDiv’
),
dcc.Input(
id = ‘ID’,
type = ‘text’,
value = ‘ABCER1’,
size = 8),

        html.Div(
            children = "Enter Test Pattern",
            className = 'textDiv'
        ),
        dcc.Input(
            id = 'pattern_desc',
            type = 'text',
            value = 'Sample',
            size = 20),
                
         html.Div(
            children = "Enter File OutPut Path:",
            className = 'textDiv'
        ),
        dcc.Input(
            id = 'file_path',
            type = 'text',
            value = '',
            size = 30),

        html.Button(
            id = 'submit',
            n_clicks = 0,
            children = 'Search'
        )
    ]
),

  html.Div(
    id = 'tableDiv',
    children = dash_table.DataTable(
        id = 'table',
        #columns = something, ## *** Not sure how to output 
                    the columns dynamically here ***
        style_table={'overflowX': 'scroll'},
        style_as_list_view=True,
        style_header={'backgroundColor': 'white','fontWeight': 
            'bold'},
         ),
        className = 'tableDiv'
    )
  ]
)

  # callback to update the table
  @app.callback([Output('table', 'data'),Output('table', 'columns')]
          [Input('submit', 'n_clicks')],
          [State('ID', 'value'),  State('pattern_desc', 'value'), 
        State('file_path', 'value')])
   def update_table(n_clicks, ID, pattern_desc, file_path):

            df = someFunc(ID, pattern_desc, file_path)
      mycolumns = [{'name': i, 'id': i} for i in df.columns]
  	 
      return html.Div([
  	        dt.DataTable(
  		id='table',
  		columns=mycolumns,
  		data=df.to_dict("rows")
         )
  	])

So in this case the function someFunc which takes the 3 input arguments returns a pandas
dataframe which can have different columns based on the inputs. Thus the app layout should display
those columns as given by the output of the callback function dynamically based on the inputs.
Not Sure How I can achieve that. Any help will be appreciated. When I run this, I am getting the data generated through the function to the file, but dash is not able to
generated the table on webpage. I get the following error:

dash.exceptions.InvalidCallbackReturnValue: The callback …table.data…table.columns… is a multi-output.
Expected the output type to be a list or tuple but got Div([DataTable(columns=[{‘name’: ‘pattern_desc’, ‘id’: ‘pattern_desc’}, …

2

Your callback has been setup with two outputs. This means you need to be returning a list or tuple of length two, as indicated by the error message.

3

Thank you nedned. Yes was trying to know how to create both of them as a list/tuple.

That part of the code I am not getting.

4

hey stan i want to render the table from the dataframe based on the input in the dropdown …how can i do it …please help me…thanks in advance

csat=pd.read_sql_query(“select * from csat”,con)
csat=csat.head(10)
#csat=csat[[‘TicketNumber’,‘Score Type’]]

def generate_table(dataframe, max_rows=10):
return html.Table(
# Header
[html.Tr([html.Th(col) for col in dataframe.columns])] +

    # Body
    [html.Tr([
        html.Td(dataframe.iloc[i][col]) for col in dataframe.columns
    ]) for i in range(min(len(dataframe), max_rows))],id='table')

external_stylesheets = [‘https://codepen.io/chriddyp/pen/bWLwgP.css’]
colors = {
‘background’: ‘#111111’,
‘text’: ‘#7FDBFF’
}

app = dash.Dash(name, external_stylesheets=external_stylesheets)

app.layout = html.Div(children=[
html.Label(‘Dropdown’),
dcc.Dropdown(
options=[{‘label’:i,‘value’:i} for i in tables ],id=‘tablename’
),
generate_table(csat)
])
@app.callback(
[Output(‘table’,‘children’)],
[Input(‘tablename’,‘value’)])

def callback_a(x):
return x

if name == ‘main’:
app.run_server(debug=True)