Sharing a dataframe between plots

Dash Python
11

I had trouble with this approach. I have a multiple page app that is trying to use the shared data to build the list of options dynamically.

  1. Defined the functions to convert list to string and vice versa. To keep it the same way as the document specified, they are converted via dataframe.
def to_jsonstr(my_list):
    df = pd.DataFrame(my_list)
    print("convert list to string")
    print(df)
    jsonStr = df.to_json(orient='split')
    print('jsonStr is {}'.format(type(jsonStr)))
    return jsonStr


def from_jsonstr(jsonList):
    print("convert dataframe to list")
    print('jsonList is {}'.format(type(jsonList)))
    df = pd.read_json(jsonList, orient='split')
    print(df)
    my_list = df[0].values.tolist()
    print(my_list)
    return my_list
  1. Two callbacks are added. add_watchlist is called when “add to watch list” button is triggered, which add the new symbol to the existing list. update_dropdown is called when the “intermediate” new-watchlist" string is updated.

app = dash.Dash()

app.config.suppress_callback_exceptions = True

app.layout = html.Div(children=[
    # global hidden value
    html.Div(id='new-watchlist'),

    html.H1(children="My Stock App"),
    dcc.Location(id='url', refresh=False),
    html.Div(id='page-content')

])


# Add Ticker to New watchlist when add button is clicked


@app.callback(Output('new-watchlist', 'children'),
              [Input('add-button', 'n_clicks')],
              [State('ticker-input', 'value'),
               State('new-watchlist', 'children')]
              )
def add_watchlist(n_clicks, ticker, jsonWatchList):
    print('json Watchlist is ')
    print(jsonWatchList)

    # watchList = ['AMZN', 'GOOG', 'TSLA']
    # print(watchList)
    if(jsonWatchList is None):
        watchList = ['AMZN', 'GOOG', 'TSLA']
    else:
        watchList = from_jsonstr(jsonWatchList)
        print('watchList after json loads')
        print(watchList)
        if ticker is not None and ticker not in watchList:
            watchList.append(ticker)
        print("after add")
        print(watchList)
    outJson = to_jsonstr(watchList)
    print("outJson is")
    print(outJson)
    return outJson

# Update Options in dropdown-watchlist


@app.callback(Output('dropdown-watchlist', 'options'),
              [Input('new-watchlist', 'children')]
              )
def update_dropdown(jsonWatchList):
    watchList = from_jsonstr(jsonWatchList)
    print("in update_dropdown")
    print(watchList)
    return [{'label': i, 'value': i} for i in watchList]

I got stuck in the callback function update_dropdown was only triggered once during page load, but not when the list is changed (I can see from the view that new-watchlist is updated, but the callback is not triggered). Could someone please help?
new-watchlist is updated now to {“columns”:[0],“index”:[0,1,2,3],“data”:[[“AMZN”],[“GOOG”],[“TSLA”],[“C”]]}
image
but update_dropdown callback was not triggered by this change.
image

A more detailed log of things I’ve tried so far