using-streamlit-session-state

Use st.session_state to persist Streamlit widget values across script reruns. It stores per-user state so variables and interactions do not reset when the script executes from top to bottom on user input.

The best way to initialize Streamlit session state is using st.session_state.setdefault at the top of your app. This safely establishes default values and guards against missing keys during subsequent reruns.

Streamlit callbacks synchronize with session state by wiring on_change and on_click handlers to widgets. These handlers update session state keys directly, ensuring component changes reflect instantly across the app.

Yes, you can use Streamlit session state for multi-page apps and multi-step forms. It maintains user preferences and interaction flows by retaining per-user state as users navigate between pages or steps.

Streamlit variables reset because the framework reruns the entire script top-to-bottom on every widget interaction. Implementing st.session_state persistence prevents this reset by retaining values across reruns.

No, using Streamlit session state requires no external dependencies. It relies entirely on the built-in st.session_state object for key management, default initialization, and per-widget synchronization.