repeated callback alters Candlestick/OHLC data #241

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

import pandas as pd
import pandas_datareader as web

app = dash.Dash()

df_a = web.DataReader("AAPL", 'morningstar').reset_index()
df_t = web.DataReader("TSLA", 'morningstar').reset_index()
df = pd.concat([df_a,df_t])

app.layout = html.Div(children=[
    html.Div(children=[
        dcc.Dropdown(
                id='input',
                options=[{'label': i, 'value': i} for i in df['Symbol'].unique()],
                value='AAPL'
            )
        ], style={'width': '100px'}),

        dcc.Graph(id='graph')
])

@app.callback(Output('graph', 'figure'),
[Input('input', 'value')])
def update_candle(value):
    symbol = str(value)
    df2 = df[df['Symbol'] == symbol]
    figure = {
        'data': [{
            'x': df2['Date'],
            'open': df2['Open'],
            'high': df2['High'],
            'low': df2['Low'],
            'close': df2['Close'],
            'type': 'candlestick',
            'name': symbol
        }]
    }
    return figure

app.css.append_css({"external_url": "https://codepen.io/chriddyp/pen/bWLwgP.css"})

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