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Introduction ​

Streamlit is an open-source Python framework for building and sharing dynamic web applications, primarily designed for data science and machine learning projects.

It lets you transform Python scripts into interactive web apps in minutes, and build dynamic data apps with only a few lines of code.

Snowflake acquired Streamlit in 2022.

Why Streamlit ​

  • Simple and Pythonic: Streamlit allows you to write clean, easy-to-read code in a Pythonic way.
  • Fast, interactive prototyping: You can create interactive apps that let users explore your data and provide feedback quickly.
  • Live editing: Your app refreshes automatically as you modify your script, giving you real-time updates.
  • Free and open-source: Streamlit is completely free, and you can join its vibrant community to contribute and collaborate.

Getting Started ​

You can create a Streamlit app with just a single python module. For example, the following script displays the text Hello World! on the webpage:

python
# Filename - test.py
import streamlit as st

st.write("Hello World!")

To run this streamlit app, use:

shell
streamlit run test.py

# ALTERNATIVE
# python -m streamlit run test.py

This starts a local web server on port 8501.

GitHub Gists ​

You can run a Streamlit app using the code from a GitHub Gist as well:

shell
streamlit run https://raw.githubusercontent.com/streamlit/demo-uber-nyc-pickups/master/streamlit_app.py

Passing arguments to your app ​

There can be scenarios where you would want to pass some input arguments to your Streamlit app. To achieve this, you can pass your custom arguments after two dashes followed by a space.

NOTE

Make sure you add a space after the dashes, else the argument will be interpreted as an option to streamlit command. Also, if you omit the dashes, the arguments get interpreted as arguments to streamlit itself.

shell
streamlit run test.py -- arg1 arg2

Data Flow ​

Streamlit employs a unique data flow where the entire script is rerun from top to bottom, whenever something must be updated on the screen. This can happen in two situations:

  • Whenever you modify your app's source code, and have Run on save enabled in Development setting.
  • Whenever a user interacts with widgets in the app. For example, when dragging a slider, entering text in an input box, or clicking a button.

This is covered in more detail later in this book.