Session state with conditional widgets

orlenok · March 30, 2022, 1:58pm

It’s my first day with streamlit – apologies if the question is basic.

I am having an issue of keeping widget state for a multipage app where widgets are displayed conditionally.

Below is a minum example: as long as I stay on page 1 the choices is preserved as I modify the selection. If I move to page 2 and then go back to page 1, it get lost from the state for some reason.

Is this a bug?

Many thanks in advance

import streamlit as st

if 'choice' in st.session_state:
    st.write(f'choice is in the session state and the value is {st.session_state.choice}')
else:
    st.write(f'choice is not yet in the session state ')

navigation = st.sidebar.radio('Navigation', [1, 2])

if navigation == 1:
    st.multiselect('Choice', [1, 2, 3], key='choice')

orlenok · March 31, 2022, 8:42am

Answering my own question if it may help anyone: this seems to be an intended (but unintuitive) feature,
it is being tracked over here together with a workaround:

github.com/streamlit/streamlit

Inconsistent session state behavior when used with widgets

opened 12:51PM - 31 Jan 22 UTC

closed 01:12AM - 02 Feb 22 UTC

okld

bug needs triage

### Summary Session state in Streamlit 0.89.0 to 1.5.0 has a strange behavior… when bound to widgets (`key` parameter). ### Steps to reproduce #### First case 1. In the same script run, initialize a session state item, and display a widget bound to it. 2. Make the widget disappear (by unchecking a checkbox for instance). 3. Reload with `R`. **ISSUE: Session state item doesn't exist anymore.** 4. Reload again multiple times. **ISSUE: Session state is cleared every other run.** #### Second case 1. In a first script run, initialize a session state item. 2. In a second run, display a widget bound to the previous session state item (by checking a checkbox for instance). **ISSUE: Widget does not take value from session state.** 3. Change widget value, it updates the session state item correctly. 4. Make the widget disappear. 5. Reload with `R`. **ISSUE: Session state item resets to its initial value**. #### Code snippet Feel free to compare the following script behavior with Streamlit 0.88.0 (working session state) and Streamlit 1.5.0. Both cases are implemented. ```python import streamlit as st st.set_page_config(layout="wide") c1, c2 = st.columns(2) with c1: st.subheader("Widget session state item 1") st.write("Session state and widget setup in the same run.") st.write("When widget disappear, session state item is cleared every other run.") with st.echo(code_location="below"): if "widget_bound" not in st.session_state: st.session_state.widget_bound = "hello" st.success(f"Item added: {st.session_state.widget_bound}") else: st.info(f"Item exists already: {st.session_state.widget_bound}") # Displayed from the beginning by default if st.checkbox("Display widget", True): st.text_input("Some widget", key="widget_bound") with c2: st.subheader("Widget session state item 2") st.write("Session state setup first, then widget in another run.") st.write("Widget does not get value initial value from session state.") with st.echo(code_location="below"): if "widget_unbound" not in st.session_state: st.session_state.widget_unbound = "hello" st.success(f"Item added: {st.session_state.widget_unbound}") else: st.info(f"Item exists already: {st.session_state.widget_unbound}") # Displayed after session state initialization if st.checkbox("Display widget", False): st.text_input("Some widget", key="widget_unbound") ``` ### Is this a regression? Yes, session state with widgets worked as expected from version 0.86.0 to 0.88.0. ### Debug info - Streamlit version: 0.89.0 to 1.5.0 - Python version: 3.8.6 (pyenv)