How to prevent app from re-running before submitting form button

Using Streamlit
3

Hi @Jurgita

One way to save the state is using session_state. I tried this code and seems to be what you need:

if "option" not in st.session_state:
    st.session_state["option"] = None


with st.form("input"):
    selected_options = st.sidebar.multiselect(
        "Select option:", ["Option1", "Option2", "Option3"], default="Option1")
    text = st.text_area("Paste text here", height=350)
    submit_button = st.form_submit_button(label="Extract data")

if submit_button:
    # Check that text field is not empty
    if not text.strip():
        st.error("WARNING: Please enter text")
    else:
        with st.spinner(text = "Extracting information…"):
            sleep(3)
            st.session_state["option"] = selected_options
            st.write("You selected: {} - inside submit_button".format(selected_options))
            st.write(text)

if st.session_state["option"] is not None:
    st.write("You selected: {} - outside submit_button".format(st.session_state["option"]))

However, it seems that changing input in multiselect causes the app to re-run and clear the output before clicking the button.

Yes, this is a fundamental property of the Streamlit architecture. You can use cache, session_state or IO operations to create an state machine or applications that preserve the state and other logics. I recommend to read this comment that is related about this characteristic