checkbox value does not get updated when using a session_state value after reruns

[Dylanlang04]

Summary

If you create a checkbox and set its value param to a session_state value then use a button with a callback on its on_click param and update that session_state value, after the rerun the checkbox does not get updated despite the value being EXPLICITLY True or False.

Steps to reproduce

Code snippet:

def select_all(index):
    st.session_state[f"test"] = True

def update_checkbox():
    st.session_state["test"] = not st.session_state["test"]
if "test" not in st.session_state.keys():
        st.session_state["test"] = False
index = 1
print(f"VALUE: {st.session_state["test"]}")
st.checkbox(
    label=f"{index}",
    value=st.session_state["test"],
    key=f"checkbox_{index}",
    on_change=update_checkbox,
)
st.button(
    label="test2",
    on_click=select_all,
    args=[index]
)

Screenshot(s):

If applicable, please provide the steps we should take to reproduce the bug:

just create a local web app with test.py as a page in app.py

Expected behavior:

When the button is clicked the checkbox should reflect the value being explicitly set in the value param

Actual behavior:

Does not update the checkbox, (the value is actually being updated, its just not being rerendered.)

Is this a regression?

That is, did this use to work the way you expected in the past?
yes, this was never an issue.

Debug info

Streamlit, version 1.51.0

• OS version: Windows 11
• Browser version: Google Chrome Version 141.0.7390.123

Additional information

[sfc-gh-dmatthews]

Thanks for the report! In version 1.50.0 the behavior of st.checkbox changes as part of a larger migration. This will be better documented in the next version as we get closer to completing the behavior change for all widgets.

As of version 1.50.0, if you set a key for st.checkbox it's identity will only depend on the key and not its other parameters. Previously, if you changed the initial value of a checkbox, it would destroy the previous instance and create a new one, causing the appearance of an "update."

The recommended pattern is to directly control the value of a widget through its key in Session State, not its initial value. If you follow this best practice, you will get the same result before and after version 1.50.0.

import streamlit as st

def make_true(index):
    st.session_state[f"checkbox_{index}"] = True

def make_false(index):
    st.session_state[f"checkbox_{index}"] = False

def toggle(index):
    st.session_state[f"checkbox_{index}"] = not st.session_state[f"checkbox_{index}"]

def show_checkbox(index):
    st.session_state.setdefault(f"checkbox_{index}", False)
    st.session_state[f"checkbox_{index}"]
    st.checkbox(f"Checkbox {index}", key=f"checkbox_{index}")

    st.button(f"Make True {index}", on_click=make_true, args=(index,))
    st.button(f"Make False {index}", on_click=make_false, args=(index,))
    st.button(f"Toggle {index}", on_click=toggle, args=(index,))

for i in range(3):
    show_checkbox(i)

I'll close this as intended behavior and reference another issue we're leaving open until we get the change and docs transition completed. streamlit/streamlit#12880