ui.update_radio_buttons doesn't allow for no selection unless choices field is provided #2400

Activity

1. schloerke commented on Aug 1, 2026

   

   schloerke

   on Aug 1, 2026

   Collaborator

   More actions

   Confirmed — this is not working as intended, and there is a one-word workaround: pass selected=[] instead of selected="".

   Reprex

   # app.py
   from shiny import App, Inputs, Outputs, Session, reactive, render, ui
   
   CHOICES = {"a": "Apple", "b": "Banana", "c": "Cherry"}
   
   app_ui = ui.page_fluid(
       ui.input_radio_buttons("rb", "Fruit", CHOICES, selected="a"),
       ui.input_action_button("clear_empty_str", 'selected=""'),
       ui.input_action_button("clear_with_choices", 'choices=..., selected=""'),
       ui.input_action_button("clear_empty_list", "selected=[]"),
       ui.output_code("val"),
   )
   
   
   def server(input: Inputs, output: Outputs, session: Session):
       @render.code
       def val():
           return repr(input.rb())
   
       @reactive.effect
       @reactive.event(input.clear_empty_str)
       def _():
           ui.update_radio_buttons("rb", selected="")
   
       @reactive.effect
       @reactive.event(input.clear_with_choices)
       def _():
           ui.update_radio_buttons("rb", choices=CHOICES, selected="")
   
       @reactive.effect
       @reactive.event(input.clear_empty_list)
       def _():
           ui.update_radio_buttons("rb", selected=[])
   
   
   app = App(app_ui, server)

   Clicking each button in turn (fresh reload before each):

   initial                         input.rb() = 'a'
   update(selected="")             input.rb() = 'a'      checked=['a']    <- no-op, the bug
   update(choices=…, selected="")  input.rb() = None     checked=[]       <- your workaround
   update(selected=[])             input.rb() = None     checked=[]       <- simpler workaround
   

   Root cause

   It is on the client. RadioInputBinding.setValue only clears the group when it receives an empty array; anything else is treated as a value to look up by selector (srcts/src/bindings/input/radio.ts):

   setValue(el, value) {
     if (Array.isArray(value) && value.length === 0) {
       $('input:radio[name="' + $escape(el.id) + '"]').prop("checked", false);
     } else {
       $('input:radio[name="' + $escape(el.id) + '"][value="' + $escape(value) + '"]')
         .prop("checked", true);
     }
   }

   With selected="" the selector becomes [value=""], which matches no radio, so .prop("checked", true) is applied to an empty set. Nothing is unchecked and the previous selection survives.

   The Python side forwards "" faithfully — _update_choice_input builds {"value": selected} and drop_none() only strips None, so "" does reach the browser. It just does not mean anything there.

   Passing choices= works only incidentally: that branch regenerates the entire options HTML (with no checked attribute) and replaces the DOM, which clears the selection as a side effect.

   Suggested fix

   Either treat an empty string as "clear" in setValue:

   if (value === "" || (Array.isArray(value) && value.length === 0)) {

   or normalize on the Python side in _update_choice_input (map selected == "" to []). The first also fixes update_checkbox_group, which routes through the same binding shape.

   Whichever way it goes, update_radio_buttons' selected parameter is currently typed Optional[str], so the working workaround (selected=[]) is not expressible without a type-checker complaint — worth widening the annotation or documenting the supported "clear" sentinel.

   Verified against shiny 1.7.1.dev6 / py-shiny main.

   ---

   This repo is the documentation site; the behavior is in the shiny package itself, so this should be moved to posit-dev/py-shiny.
2. schloerke commented on Aug 1, 2026

   

   schloerke

   on Aug 1, 2026

   Collaborator

   More actions

   Thank you for the Issue, @nvd2291 !
3. schloerke

   transferred this issue fromposit-dev/py-shiny-siteon Aug 1, 2026
4. github-actions

   added

   needs-triage

   on Aug 1, 2026
5. posit-shiny-automation

   added

   Priority: MediumValid bug or well-defined request with moderate impact or a workaround.Valid bug or well-defined request with moderate impact or a workaround.

   ai-triage:doneMarks an issue whose AI triage workflow is complete.Marks an issue whose AI triage workflow is complete.

   on Aug 6, 2026