Widgets inside expander display wrong state when set by st.session_state

[jcadams]

Summary

Widgets inside of an expander do not show the correct state if all the following are true:

1. They have been initialised using st.session_state
2. Code that is run after an if st.checkbox() is run
3. They have not been opened before 2) occurs

The variable set to the widget is correct but the displayed value is not.

Steps to reproduce

import streamlit as st

defaults = {'foo':5,'bar':10}

for default in defaults:
    if default not in st.session_state:
        st.session_state[default] = defaults[default]

foo = st.number_input('foo',key='foo')

with st.expander('bar'):
    bar = st.number_input('bar',key='bar')

if st.checkbox('foo + bar'):
    st.write(foo + bar)

Steps to reproduce:

• Run the app
• Don’t open the expander
• Click the checkbox
• Now open the expander

Expected behavior:
The widget inside the expander correctly shows its value: 10

Actual behavior:
The widget inside the expander displays its value as 0, even though the variable it is set to has the correct value (10)

Debug info

• Streamlit version: 1.24.0
• Python version: 2.11.4
• OS version: WIndows 10
• Browser version: Chrome 116.0.5845.188

[Asaurus1]

Confirmed on 1.26.0 on Linux as well.

The behavior is also present if you do the following steps:

1. • Run the app
2. • Don’t open the expander
3. • Change the value of the “foo” number_input either using keyboard entry or the +/- buttons
4. • Now open the expander

It does NOT happen if you add st.tabs to the page and replace step 3 with “change from one tab to another”.

It does NOT happen if you replace the expand box with st.tabs and put the “bar” number-input on a second tab.

So it seems the bug requires:

• “Fresh” session state (where the “bar” widget has not yet been drawn)
• An input element in an expand-box
• An update to page state?

I suspect this is a problem with the front-end since on the python side the app is behaving as expected. I am not a JS-familiar person so I can’t help much other than confirm the unexpected behavior.

[Asaurus1]

This also happens for other inputs besides number_input:

Steps to reproduce:

import streamlit as st

defaults = {'foo':5,'bar':"default"}

for default in defaults:
    if default not in st.session_state:
        st.session_state[default] = defaults[default]

foo = st.number_input('foo',key='foo')
with st.expander('bar'):
    bar = st.text_input('bar', key='bar')

if st.checkbox('foo + bar'):
    st.write(str(foo) + bar)

@jcadams have you reported this on the bugtracker?