Prevent app refresh after form_submit_button

Using Streamlit
1

I am trying to create a form where the user can select certain options with checkboxes. I want to then use these choices further on in my code.
The problem is that for some reason, nothing within the “if submit_button” loop is being executed. why?

with st.form(key="source_selection"):  # Create a form
    st.write("Please choose the options you want to use.")
    for option in options:
        st.checkbox(option, key='checkbox_' + option)
    submit_button = st.form_submit_button(label="Submit")
    if submit_button:  # Check if submit button is clicked
        print('SUBMITTED')
        selected_options = [option for option in options if st.session_state['checkbox_' + option]]
        st.write("Post-submit selected options:")
        st.write(selected_options)
        if selected_options:
            # update session state with selected options
            st.session_state.app_state.selected_options = selected_options
            st.write(f"Selected Options: {', '.join(selected_options)}")
            send_selected_sources_to_backend(selected_options)
        else:
            st.warning("Please select at least one option.")
2

It seems like it works fine to me – here’s my attempt to make a complete script

import streamlit as st

options = ["option1", "option2", "option3", "option4", "option5"]

if "app_state" not in st.session_state:
    st.session_state.app_state = {}
    st.session_state.app_state["selected_options"] = []


def send_selected_sources_to_backend(selected_options):
    st.info(f"Sending selected options to backend: {selected_options}")


with st.form(key="source_selection"):  # Create a form
    st.write("Please choose the options you want to use.")
    for option in options:
        st.checkbox(option, key="checkbox_" + option)
    submit_button = st.form_submit_button(label="Submit")
    if submit_button:  # Check if submit button is clicked
        print("SUBMITTED")
        selected_options = [
            option for option in options if st.session_state["checkbox_" + option]
        ]
        st.write("Post-submit selected options:")
        st.write(selected_options)
        if selected_options:
            # update session state with selected options
            st.session_state.app_state["selected_options"] = selected_options
            st.write(f"Selected Options: {', '.join(selected_options)}")
            send_selected_sources_to_backend(selected_options)
        else:
            st.warning("Please select at least one option.")

st.write("selected:")
st.write(st.session_state.app_state["selected_options"])

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image1828×1856 188 KB

It’s possible that it’s not working in your case because there’s something besides the code that you’ve posted is breaking something.