streamlit session state

Guri Bee

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19-10-2024

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Streamlit Session State: Your Guide to Interactive Apps

Streamlit is a popular Python library for building interactive web applications, particularly for data science and machine learning projects. One key feature that enhances interactivity and allows for persistent data within a user session is Session State. This article will delve into the nuances of Session State, providing practical examples and answering common questions from the GitHub community.

What is Streamlit Session State?

Think of Session State as a persistent dictionary that holds data specific to each user's session. This data is preserved across page refreshes and navigation within your Streamlit app, enabling features like:

• Form Input Persistence: Remember user inputs across multiple steps in a multi-page form.
• State Management: Keep track of app variables, such as counters, selections, or progress indicators.
• User Preferences: Store personalized settings or data for individual users.

How to Use Session State

Streamlit provides two ways to access Session State:

1. The st.session_state object: This is the most common way to access Session State. You can directly access and modify values within the st.session_state dictionary.

   import streamlit as st
   
   st.title("Simple Counter App")
   
   if 'count' not in st.session_state:
       st.session_state.count = 0
   
   st.button("Increment", on_click=lambda: st.session_state.count += 1)
   st.write(f"Current Count: {st.session_state.count}")
   

   In this example, the counter value is stored in st.session_state.count. Clicking the "Increment" button updates the counter value, which persists across subsequent clicks.

2. The @st.experimental_singleton decorator: This decorator creates a single instance of a function or class, ensuring that the data is consistent across multiple calls.

   import streamlit as st
   
   @st.experimental_singleton
   def get_data():
       # Perform data loading or other expensive operations here
       return "Loaded data"
   
   st.write(get_data()) 
   

   Here, the get_data function is only called once, and the returned value is stored for subsequent calls, saving computational resources.

Common Questions and Answers

Q: What is the difference between st.session_state and st.experimental_singleton?

A: While both manage persistent data, st.session_state is a global dictionary for your app, while st.experimental_singleton creates a single instance of a function or class. Choose st.session_state for storing simple data or user-specific settings, and st.experimental_singleton for functions or classes requiring consistent results across multiple calls.

Q: How do I clear Session State?

A: You can clear the entire Session State using: st.session_state.clear() or clear specific items using: del st.session_state['key'].

Q: How do I use Session State with multiple users?

A: Session State is tied to individual user sessions. If you need to share data across users, consider using a database or a shared file system.

Q: When should I use Session State?

A: Use Session State when you need to store data that needs to persist across user interactions, such as:

• User inputs across multiple pages
• App-specific settings or preferences
• State variables for interactive elements

Conclusion

Streamlit Session State is a powerful tool for building dynamic and interactive web applications. Understanding its functionality and how to use it effectively can greatly enhance your Streamlit apps.

This article has provided a basic introduction to Session State and answered common questions, but the possibilities are endless. Explore the Streamlit documentation and GitHub community resources for more advanced examples and real-world applications of Session State.