app.py

# Import convention
import streamlit as st

organ = st.selectbox('Organ', ['Brain', 'Thorax'], index=None)
modality = st.selectbox('Modality', ['Magnetic Resonance Imaging', 'Computed Tomography'], index=None)
style = st.selectbox('Style', ['Picasso', 'Van Gogh'], index=None)

prompt_lst = [organ, modality, style]
if None not in prompt_lst:
    prompt = ','.join(prompt_lst) 
    print(prompt)