Using callbacks and session state in Streamlit forms

form_callback_demo_simple.py

import streamlit as st
import pandas as pd
import numpy as np

st.write('`Simple form callback demo`')
st.subheader('Constraints Solver')

state = st.session_state
if 'is_modified' not in state:
    state['is_modified'] = False
if 'message' not in state:
    state['message'] = 'No changes'

messageboard = st.empty()

def _change_callback():
    settings = [state.setting_1, state.setting_2, state.setting_3]
    print(settings)

    is_modified = True in settings
    state.is_modified = is_modified
    
    state.message = 'Changes: {}'.format(settings) if is_modified else 'No changes'

    print(state.message)

messageboard.info(state.message)

st.markdown('#### Settings')
with st.form('settings_form'):
    st.checkbox(label='Setting 1', value=False, key='setting_1')
    st.checkbox(label='Setting 2', value=False, key='setting_2')
    st.checkbox(label='Setting 3', value=False, key='setting_3')
    st.form_submit_button('Apply constraint settings', on_click=_change_callback)

if state.is_modified:
    st.markdown('#### Results')
    tab1, tab2 = st.tabs(["Charts","Data tables"])
    settings = {k:np.random.rand(1,5)[0] for k,v in state.items() if 'setting_' in k and v == True}
    settings_df = pd.DataFrame.from_dict(settings)
    with tab1:
        st.area_chart(settings_df)
    with tab2:
        st.write(settings_df)
else:
    st.write('Please apply one or more constraints in the form above to see outcomes...')