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

[nvd2291]

I'm not sure if this is working as intended but I'm trying to update an input_radio_button group that is dependent on another radio button group. My intention is that whenever another button in a different radio group is selected the currently selected radio button is none. The only way to achieve this when calling ui.update_radio_buttons() is to provide the choices parameter and the selected = "". I would have thought to have no selection you could simply enter selected = "" but it does not update the selected field

[schloerke]

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.

[schloerke]

Thank you for the Issue, @nvd2291 !