UI not updating when setting reactive value (pn.rx) to the empty string

[MarcSkovMadsen]

I'm on panel==1.3.8. I'm trying to update a UI progressively using pn.rx for the basic tutorial. But I'm experiencing an issue with the UI not updating when setting a reactive value (pn.rx) to the empty string.

result.rx.value="" # This line does not update the UI

result.rx.value="Some Value" # This line does update the UI

Reproducible Example

import panel as pn
from time import sleep
import random

pn.extension()

OPTIONS = ["Wind Turbine", "Solar Panel", "Battery Storage"]

# State

result = pn.rx("")
is_running = pn.rx(False)

# Transformations

def classify(image):
    sleep(2)
    return random.choice(OPTIONS)

has_result = result.rx.pipe(bool)

def _show_submit_message(result, is_running):
    return not result and not is_running

show_submit_message=pn.rx(_show_submit_message)(result, is_running)

def run_classification(_):
    result.rx.value=""
    is_running.rx.value=True
    prediction = classify(None)
    result.rx.value = f"Its a {prediction}"
    is_running.rx.value=False
    # result.rx.value=""

# Inputs: Widgets

run = pn.widgets.Button(name="Submit", button_type="primary", on_click=run_classification)

# Outputs: Views

click_submit = pn.pane.Markdown("Click Submit", visible=show_submit_message)
progress_message = pn.Row(
    pn.indicators.LoadingSpinner(
        value=True, width=25, height=25, align="center", margin=(5, 0, 5, 10)
    ),
    pn.panel("Running classifier ...", margin=0),
    visible=is_running
)

pn.Column(run, click_submit, result, progress_message).servable()

When I click the button the second, third etc. time, I would expect the result string be reset to "" in the UI at the start of the classification. But it does not happen as you can see in the video below.

reset-not-working.mp4

Alternative Version

We can also set the result to "" at the end of the classification to make the issue more clear. Instead the intermediate result "Its a Solar Panel" or similar is shown!

import panel as pn
from time import sleep
import random

pn.extension()

OPTIONS = ["Wind Turbine", "Solar Panel", "Battery Storage"]

# State

result = pn.rx("")
is_running = pn.rx(False)

# Transformations

def classify(image):
    sleep(2)
    return random.choice(OPTIONS)

has_result = result.rx.pipe(bool)

def _show_submit_message(result, is_running):
    return not result and not is_running

show_submit_message=pn.rx(_show_submit_message)(result, is_running)

def run_classification(_):
    result.rx.value=""
    is_running.rx.value=True
    prediction = classify(None)
    result.rx.value = f"Its a {prediction}"
    is_running.rx.value=False
    result.rx.value=""

# Inputs: Widgets

run = pn.widgets.Button(name="Submit", button_type="primary", on_click=run_classification)

# Outputs: Views

click_submit = pn.pane.Markdown("Click Submit", visible=show_submit_message)
progress_message = pn.Row(
    pn.indicators.LoadingSpinner(
        value=True, width=25, height=25, align="center", margin=(5, 0, 5, 10)
    ),
    pn.panel("Running classifier ...", margin=0),
    visible=is_running
)

pn.Column(run, click_submit, result, progress_message).servable()

not-working2.mp4

[philippjfr]

Nothing to do with rx it turns out, HTML and other markup panes apparently couldn't be emptied at all.