app.py

import streamlit as st
from main_page import main as main_page

# Import other pages. Assume each has a main function to run the page.
from pages.data_source_config import main as data_source_config
from pages.data_loading import main as data_loading
# Add imports for other pages similarly...

# Initialize session state for page navigation if not already set
if 'page' not in st.session_state:
    st.session_state.page = 'main_page'

# Define a function to change the page
def change_page(page_name):
    st.session_state.page = page_name

# Page selection (could also use st.sidebar for these)
st.sidebar.title("Navigation")
st.sidebar.button("Main Page", on_click=change_page, args=('main_page',))
st.sidebar.button("Data Source Configuration", on_click=change_page, args=('data_source_config',))
st.sidebar.button("Data Loading", on_click=change_page, args=('data_loading',))
# Add buttons for other pages similarly...

# Page dispatch
if st.session_state.page == 'main_page':
    main_page()
elif st.session_state.page == 'data_source_config':
    data_source_config()
elif st.session_state.page == 'data_loading':
    data_loading()
# Add elif blocks for other pages...

# The above could be optimized by mapping page names to functions