# Filling a checklist through a callback **URL:** https://community.plotly.com/t/filling-a-checklist-through-a-callback/7435 **Category:** Dash Python **Created:** [December 21, 2017, 10:20am UTC](https://community.plotly.com/t/filling-a-checklist-through-a-callback/7435 "2017-12-21T10:20:12Z") **Posts on this page:** 3 **Page:** 1
### Author: ![rauldom](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@rauldom](https://community.plotly.com/u/rauldom) #### Post date: [December 21, 2017, 10:20am UTC](https://community.plotly.com/t/filling-a-checklist-through-a-callback/7435/1 "2017-12-21T10:20:13Z")
Hello everyone! First of all, thank you for this wonderful library. I have a problem to fill a Checklist through a callback. My code is the next: ```auto import dash from dash.dependencies import Input, Output, State import dash_core_components as dcc import dash_html_components as html app = dash.Dash() app.css.append_css({'external_url': 'https://codepen.io/chriddyp/pen/bWLwgP.css'}) app.layout = html.Div( children = [ html.Div( id = 'list', children = [dcc.Checklist(id = "myList")]), html.Button('Fill Checklist', id='list-btn', n_clicks=0)] ) @app.callback( Output('myList', 'options'), [Input('list-btn', 'n_clicks')] ) def fillChecklist(n_clicks): data = [['label-1', '1'],['label-2', '2']] return [{'label': x[0] +" "+ x[1], 'value' : x[1] } for x in data] if __name__ == ' __main__': app.run_server(debug=True) #dcc.RadioItems ``` and i got: ![image](https://us1.discourse-cdn.com/flex024/uploads/plot/original/2X/3/38bc951dc1a8ec5659e91f68ea7a1bb234915ba7.png) the console shows: ```auto 127.0.0.1 - - [21/Dec/2017 04:04:07] "GET / HTTP/1.1" 200 - 127.0.0.1 - - [21/Dec/2017 04:04:11] "GET /_dash-layout HTTP/1.1" 500 - Traceback (most recent call last): File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1997, in __call__ return self.wsgi_app(environ, start_response) File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1985, in wsgi_app response = self.handle_exception(e) File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1540, in handle_exception reraise(exc_type, exc_value, tb) File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\_compat.py", line 33, in reraise raise value File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1982, in wsgi_app response = self.full_dispatch_request() File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1614, in full_dispatch_request rv = self.handle_user_exception(e) File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1517, in handle_user_exception reraise(exc_type, exc_value, tb) File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\_compat.py", line 33, in reraise raise value File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1612, in full_dispatch_request rv = self.dispatch_request() File "C:\Users\Raul\Anaconda3\lib\site-packages\flask\app.py", line 1598, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args) File "C:\Users\Raul\Anaconda3\lib\site-packages\dash\dash.py", line 165, in serve_layout cls=plotly.utils.PlotlyJSONEncoder), File "C:\Users\Raul\Anaconda3\lib\json\ __init__.py", line 237, in dumps **kw).encode(obj) File "C:\Users\Raul\Anaconda3\lib\site-packages\plotly\utils.py", line 136, in encode encoded_o = super(PlotlyJSONEncoder, self).encode(o) File "C:\Users\Raul\Anaconda3\lib\json\encoder.py", line 198, in encode chunks = self.iterencode(o, _one_shot=True) File "C:\Users\Raul\Anaconda3\lib\json\encoder.py", line 256, in iterencode return _iterencode(o, 0) File "C:\Users\Raul\Anaconda3\lib\site-packages\plotly\utils.py", line 204, in default return _json.JSONEncoder.default(self, obj) File "C:\Users\Raul\Anaconda3\lib\json\encoder.py", line 179, in default raise TypeError(repr(o) + " is not JSON serializable") File "", line 52, in __repr__ File "", line 52, in File "", line 52, in __repr__ ....... RecursionError: maximum recursion depth exceeded while calling a Python object 127.0.0.1 - - [21/Dec/2017 04:04:11] "GET /_dash-dependencies HTTP/1.1" 200 - 127.0.0.1 - - [21/Dec/2017 04:04:11] "GET /favicon.ico HTTP/1.1" 200 - ``` When I change the dcc.Checklist() for dcc.RadioItems() the code worrks fine: ![image](https://us1.discourse-cdn.com/flex024/uploads/plot/original/2X/2/28c9cae1df41e865bfe587c4b10ba4f9789c888f.png) I don’t know what I’m doing wrong or if it’s a kind o bug. I would greatly appreciate your help or I want to know if someone has another way to fill a checklist. Thank’s ---
### Author: ![nedned](https://sea2.discourse-cdn.com/flex024/user_avatar/community.plotly.com/nedned/32/8795_2.png) [@nedned](https://community.plotly.com/u/nedned) #### Post date: [December 22, 2017, 1:47pm UTC](https://community.plotly.com/t/filling-a-checklist-through-a-callback/7435/2 "2017-12-22T13:47:07Z")
The problem is that the checklist component must have an initial value provided for its `values` attribute. Even though you’re generating the value of that attribute with the callback, the component must have a specified value on initialisation. `values=[]` seems to make it happy. Edit: I’ve just filed an issue over on the dash-core-components repository about this – [https://github.com/plotly/dash-core-components/issues/133](https://github.com/plotly/dash-core-components/issues/133) ---
### Author: ![chriddyp](https://sea2.discourse-cdn.com/flex024/user_avatar/community.plotly.com/chriddyp/32/16855_2.png) [@chriddyp](https://community.plotly.com/u/chriddyp) #### Post date: [December 22, 2017, 5:32pm UTC](https://community.plotly.com/t/filling-a-checklist-through-a-callback/7435/3 "2017-12-22T17:32:00Z")
I commented about this in the issue above ([https://github.com/plotly/dash-core-components/issues/133#issuecomment-353641641](https://github.com/plotly/dash-core-components/issues/133#issuecomment-353641641)). Thanks for reporting and triaging!