St.radio on_change not working as intended or implementation incorrect

[fabischw]

Hello, I’ve tried tried fixing this error for an day now and have unfrtunetly not gotten a response in the discord so I’ll just ask here.

I’m experiencing an issue where the streamlit radio on_change fires the function without the value actually changing but rather on the initial page render which is causing other problems in my app.
I do not know whether my implementation is just not ideal or if it’s an actual bug with the st.radio on_change parameter.

To reproduce:
download / copy the files in here
and run the home.py file using ‘streamlit run home.py’

Is this an unintended bug or am I just not understanding the st.radio correctly ??
Would appreciate any help on this ;D

[mathcatsand]

I think the main part of your question is covered by separating the function assigned to on_change and its arguments.

You have:

st.radio(...on_change=update_settings("number_input"))

There is a separate keyword to pass the arguments. This is so on_change gets assigned a function object and not the output of that function. (Note the extra comma to pass the argument as a tuple of size 1.)

st.radio(...on_change=update_settings, args=("number_input",))

There is also another fact that the radio button does not output its value until after the callback function is run. So number_inpt_choice will not have the intended value until after the page loads.

If you set the radio button to have key="number_inpt_choice" then upon clicking it (and instantaneously before the on_change function is run), you can access st.session_state.number_inpt_choice within the on_change function if you need to.

[fabischw]

Thank you so much, got the implementation working and it all makes sense now, can finally move onto the next part of my app after finally getting this error resolved ;D