using-streamlit-session-state

Initialize st.session_state with setdefault, attach widgets using the key parameter, and access values directly in your page logic. This prevents variables from resetting on every script interaction and maintains stable per-user experiences.

Streamlit reruns the entire script on every interaction, resetting non-persistent variables. You need session_state to persist values across reruns, enabling stable state management for multi-page apps, complex widgets, and dynamic dashboards.

Safely initialize session state in Streamlit by using st.session_state.setdefault("key", default) before accessing the value. This prevents KeyError and race conditions during script reruns by ensuring the key exists prior to widget rendering.

You can share session state across multiple pages in a Streamlit app using st.session_state. It enables per-page and multi-page state sharing, ensuring state consistency for per-user values throughout dynamic dashboards and complex widget interactions.

Implement callbacks in Streamlit by reading and updating st.session_state directly within your callback functions. Attach widgets with a key parameter, then use these callbacks to handle state changes safely without breaking reruns.

You need session state for a Streamlit dashboard when maintaining state consistency and per-user values across reruns is crucial. It is specifically required for multi-page apps, complex widgets, and dynamic dashboards to prevent data loss.