CODEWITHSUNDEEP
google-colaboratoryipywidgets
Lev
Lev

Reputation: 6667

ipywidgets properties not updated in Colab

I'm running the following code:

button = widgets.ToggleButton(description='Button')
display.display(button)
for i in range(100):
  print(button.value)
  time.sleep(0.5)

No matter how many times I toggle the button, the value that is printed is always False, even though button.value is True if I try to print it in the next cell. How can I fix this?

Upvotes: 0

Views: 58

Answers (1)

Wayne
Wayne

Reputation: 9984

In your example, you wanted a loop iterating for a set amount of cycles to respond...
The problem with your implementation though is a for loop is blocking for ipywidgets' event loop, see here. So it blocks and doesn't allow the value change to show up. Luckily, Jupyter is in a browser and so in modern Jupyter (debatable if Google Colab is that at this time) with modern Python you can now use asyncio, as pointed out there.

This tested & veridied-working code works with asyncio to do more or less what your code snippet seemed to want to do:

import asyncio
import ipywidgets as widgets
from IPython.display import display, clear_output
import time

button = widgets.ToggleButton(description='Button')
output = widgets.Output()
display(button, output)

async def update_status():
    for i in range(100):
        with output:
            clear_output()
            print(f"Iteration: {i+1} / 100")
            print(f"Button Value: {button.value}")
        await asyncio.sleep(0.5)  # Use asyncio.sleep for asynchronous delay

asyncio.ensure_future(update_status());


You don't say why you want to do this though and it may very well be there is a better approach compatible with ipywidgets and modern browser-based event loops. You may wish to refer to other discussions referencing there (or related stuff here or here) to avoid making an XY problem for yourself.

Related Helpful Aside that came up on the journey:

In case it helps others who end up here, here is a simpler example to respond to clicks to in modern Jupyter. (It also addresses that to handle output properly you have to channel it and that presently JupyterLab is the best for debugging things involving ipywidgets. For all these reasons, I'm leaving it here even though the answer above more directly gets at the OP's issue.)
I don't use Google Colab; however, in modern Jupyter this works to toggle the value:

import ipywidgets as widgets
from IPython.display import display, clear_output

# Create a ToggleButton widget with an initial value of False
toggle_button = widgets.ToggleButton(value=False, description='Toggle Me')

# Create an output widget to display the value
output = widgets.Output()

# Display the widgets
display(toggle_button, output)

# Define a function to be called when the button's value changes
def on_toggle_change(change):
    with output:
        clear_output()  # Clear previous output
        print(f"New value: {change['new']}") 

# Observe changes to the button's value and call the function
toggle_button.observe(on_toggle_change, names='value')

So this uses an ipywidgets button to do something.
And if you don't use an Output Widget, the print() would go to the Log Console in JupyterLab. Presently, you really get no feedback with Jupyter Notebook 7+. Therefore, when working with ipywidgets, JupyterLab is best used when debugging because of the Log Console access.

Upvotes: 0

Related Questions