Introduction to Streamlit Beginner

Streamlit is an open-source Python framework that lets you build web applications in minutes. Write pure Python - no HTML, CSS, or JavaScript required. It is designed for data scientists and ML engineers who want to turn data scripts into shareable web apps quickly.

What is Streamlit?

Streamlit transforms Python scripts into interactive web applications. Every time you save your script, the app updates automatically (hot reload). It was acquired by Snowflake in 2022 and remains open-source with a thriving community.

Why Streamlit?

What You Can Build

• Data Dashboards: Interactive charts, filters, and real-time data views
• ML Model Demos: Upload data, run predictions, visualize results
• Internal Tools: Admin panels, data entry forms, reporting tools
• Data Exploration: Upload CSVs, filter, sort, and visualize datasets
• AI Chat Interfaces: Chat UIs for LLMs with streaming support
• Documentation: Interactive tutorials and code walkthroughs

How Streamlit Works

Streamlit re-runs your entire Python script from top to bottom every time the user interacts with a widget. This is the execution model:

1. User opens the app

   The entire script runs from top to bottom, rendering all UI elements.

2. User interacts with a widget

   When a user clicks a button, moves a slider, or enters text, the script re-runs from the top.

3. Cached values persist

   Functions decorated with @st.cache_data or @st.cache_resource skip re-computation across runs.

4. Session state persists

   Use st.session_state to store values that persist across re-runs within a user session.