Streamlit selectbox that works as intended

stateful_selectbox.py

 #
 # This gist solves 2 problems
 # 1. Streamlit selectbox sometimes does not return correct value correpsonding to what user selected.
 #    This is a very finicky behavior where the user-selected option, occasionally, reverts back to older option
 #    and thus violating WYSIWYG. This function fixed it
 # 2. In multi-page apps, the user-selected values in selectbox gets lost when user switches to another page.
 #    This function saves the state and helps these widget maintain state even in multi-page apps
 #
 def stateful_selectbox(
        name, 
        dropdown_options, 
        widget_key, 
        default_index=0
    ):
    twin_key = widget_key + '_twin' #User variables (like ..._twin) are not lost when switching pages whereas widget keys are lost
    
    selected_index = default_index
    if widget_key not in st.session_state:
        if twin_key in st.session_state:
            # This condition happens when the user has returned back after visiting a new page
            widget_value = st.session_state[twin_key]
            #st.session_state[widget_key] = widget_value #FIX: This will be set by the st.selectbox() call below
            try:
                selected_index = dropdown_options.index(widget_value)
            except:
                selected_index = 0
                del st.session_state[twin_key]
    else:
        assert twin_key in st.session_state
        widget_value = st.session_state[widget_key]
        del st.session_state[widget_key]
        try:
            selected_index = dropdown_options.index(widget_value)
        except:
            selected_index = 0
        
    #st.write('selectbox called with options={} key={} index={}'.format(dropdown_options, widget_key, selected_index))

    widget_value = st.selectbox(
        name,
        options=dropdown_options,
        key=widget_key,
        index=selected_index
    )
    st.session_state[twin_key] = widget_value

    return widget_value