What is Streamlit in Python? A Beginner-Friendly Guide

If you’re learning Python and you’ve reached a point where scripts and terminal outputs feel limiting, here’s the thing: Streamlit is often the bridge between “I wrote some Python” and “I built something people can actually use.”

Streamlit lets you turn plain Python code into interactive web apps with almost zero frontend work. No HTML, no CSS, no JavaScript. Just Python.

This article is written for Python beginners who understand basic concepts like variables, functions, and libraries, and want to build something visual and practical. We’ll walk through what Streamlit is, how it works, why it exists, and how you can start using it confidently. So, let us get started!

Quick Answer:
Streamlit is an open-source Python library that lets you build interactive web applications directly from Python scripts, without needing HTML, CSS, or JavaScript, making it ideal for beginners who want to turn data or logic into visual, shareable apps quickly.

What is Streamlit in Python?

Streamlit was launched in 2019 as a tool for data scientists and developers to create web apps using only Python. Streamlit is an open-source Python framework used to build interactive web applications directly from Python scripts.

In simple terms:

• You write Python code
• Streamlit runs it
• That code instantly becomes a web app

You don’t design pages. You don’t manage routes. You don’t worry about frontend frameworks. You focus on logic and data, and Streamlit handles the UI layer for you.

Its core idea is that “apps were just scripts”: you don’t need to learn HTML/JS – instead, you write Python code and Streamlit turns it into an interactive webpage. 

Why Use Streamlit?

You might ask, “Why would I use Streamlit instead of just writing a script or notebook?” The biggest advantages are interactivity and simplicity. With Streamlit, your Python script instantly becomes a web app with minimal effort.

• Instant visual feedback: When you run a Streamlit app, any code that draws charts or writes output is shown live in the browser. You can place text, plots, data tables, and widgets on it using st. commands.
  
• Automatic updates: Streamlit watches for changes. Whenever you edit and save your script (or a user manipulates a widget), Streamlit will rerun the entire script from the top. This reactive flow ensures the app UI is always up-to-date with the code.
  
• Built-in components: Streamlit comes with many ready-made UI elements for data apps. This includes layout helpers, text formatting, charts, images, and widgets (sliders, buttons, file uploaders, etc.).
  
• No web framework needed: Unlike general web frameworks, you don’t have to set up routes, HTML templates, or styling. One of Streamlit’s selling points is that you can “build interactive web apps using only Python”.
  
• Easy sharing and deployment: Once an app is written, you can share it as easily as sharing code. Streamlit offers a free community cloud where you push your GitHub repo and deploy with one click.
  
• Great Community: Streamlit’s community and adoption have grown rapidly. By late 2021, it had millions of users and downloads. In fact, by 2021 it saw 4.5 million downloads and 16,000 stars on GitHub; by 2023 it reported over 20,000 GitHub stars and 10 million app views, with companies like Uber, Spotify, NASA, and WHO using it.

In short, Streamlit is popular because it lets you go from Python script to a shareable interactive app in minutes, all with minimal effort. 

If you want to read more about how Python works and its use cases, consider reading HCL GUVI’s Free Python eBook: A Beginner’s Guide to Coding & Beyond, which covers the key concepts of Python, including OOPs, File Handling, and even database connectivity.

Getting Started with Streamlit

Getting started is very simple. 

1. Install Streamlit. 

In a terminal or command prompt, run:

pip install streamlit

This installs the Streamlit library (along with its dependencies) into your Python environment. It works with any Python setup (virtualenv, Conda, etc.).

2. Write a Streamlit script. 

Create a new Python file (e.g. app.py). At the top, import Streamlit: import streamlit as st. Then you can use Streamlit commands in that script to build your interface. For example:

import streamlit as st

st.title("My First Streamlit App")

st.write("Hello, welcome to my app!")

x = st.slider("Select a value", 0, 100, 50)

st.write(f"You selected {x}")

Each st. function adds something to the page. In this snippet, st.title sets a large title, st.write displays text, and st.slider creates an interactive slider. (We’ll explain more of these commands below.)

3. Run your app. 

In the terminal, navigate to the directory of your script and type:

streamlit run app.py

This command starts a local web server and opens your app in the browser. You should see the title, text, and slider from the code above. Try moving the slider and notice that the page updates the selected value. Under the hood, Streamlit reruns your script each time you change something. You can stop the app by pressing Ctrl+C in the terminal.

4. Develop interactively. 

With the app running, edit app.py in your editor (for example, change the title or add more widgets) and save. Streamlit will usually ask “Rerun app?” – click “Always rerun” (or it may auto-update). Your changes appear almost instantly in the browser. 

This tight feedback loop is a major feature: one doc notes that you “type some code, save it, try it out live, then type some more code, save it, try it out”.

If you are just now starting your journey on Python, then this blog is for you – Python Beginner Roadmap: Basics to Web in 3 Months

Building a Simple App

Let’s walk through a very basic example to see Streamlit in action:

1. Create app.py:

import streamlit as st

st.title("My First App")

st.write("This is a simple Streamlit application.")

number = st.slider("Pick a number", 0, 100, 25)

st.write(f"You selected {number}")

• We import Streamlit (import streamlit as st).
  
• st.title and st.write add static text.
  
• st.slider creates a slider widget for user input.=

2. Run the app:

In the terminal, run:
streamlit run app.py

The browser will open showing “My First App” as a header, the explanatory text, and a slider. As you move the slider, the number displayed updates automatically. This interactivity happens without any extra wiring – Streamlit reruns the script behind the scenes whenever the slider value changes.

3. Add more components:

You can keep expanding the app. For example, add:

name = st.text_input("Enter your name")

if st.button("Greet"):

    st.write(f"Hello, {name}!")

This adds a text box and a button. When the user types a name and clicks the button, the greeting appears. Again, this requires no web coding – just Python.

Each new st. call you add will appear in your app in that order. This step-by-step code approach makes it very clear how the UI is built. According to the official tutorial, with just a handful of Streamlit commands, “raw CSV files can be transformed into an interactive web app”, illustrating how little code is needed to go from data to a working app.

Tips and Best Practices For Using Streamlit in Python

• Run and Save Often: Keep Streamlit running while you code. It’s best to split your screen or window so you can edit code in an editor on one side and immediately see changes in the browser. Save the Python file frequently; Streamlit detects the save and asks if it should rerun. For convenience, enable “Always rerun” so you don’t have to confirm each time.
  
• Use Markdown: st.markdown() lets you write Markdown text, which can include headings, bold/italic text, lists, and links. This is handy for formatting instructions or explanations in your app.
  
• Cache Data: If your app loads or computes expensive data (like reading a large file or training a model), use @st.cache_data (or older @st.cache) to cache the result. This way, Streamlit won’t redo the computation on every rerun, which keeps the app responsive. (This is an advanced feature you can learn about later.)
  
• Check the Console: Streamlit outputs helpful logs in the terminal. If something breaks, look at the terminal for error messages. Also, Streamlit shows your script name and lines it is running in the browser’s status bar; this can help with debugging.
  
• Keep It Simple: For a beginner-friendly experience, stick to fundamental features first. Don’t try to implement complex web designs immediately. Focus on quickly turning your Python logic into visible elements.

If you want to learn more about Python through a structured course material, consider enrolling in HCL GUVI’s Free Self-Paced IITM Pravartak Certified Python Course that lets you start from scratch and gradually move towards the level where you can write programs to gather, clean, analyze, and visualize data.

Conclusion

In conclusion, Streamlit turns your Python scripts into interactive web apps with minimal effort. It’s open-source, designed for data people, and comes with a rich set of UI elements out of the box. 

To use it, you simply install it via pip, write a script using import streamlit as st, and include commands like st.title(), st.write(), charts, and widgets. Running streamlit run your_app.py launches the app locally. You can then explore your data and code in an iterative, visual way.

If you’ve learned the basics here, you can now start experimenting: try building a small dashboard for your data or a simple ML model demo. Streamlit’s documentation and community gallery have many more examples to inspire you. As you grow more comfortable, you can explore advanced features like caching, session state, or even deploying to Streamlit’s cloud platform.

FAQs

1. What is Streamlit used for in Python?

Streamlit is used to build interactive web applications using only Python. It’s commonly used for data visualization, dashboards, and showcasing machine learning models without frontend development.

2. Is Streamlit good for Python beginners?

Yes. Streamlit is beginner-friendly because you don’t need HTML, CSS, or JavaScript. If you know basic Python, you can start building apps almost immediately.

3. Do I need web development knowledge to use Streamlit?

No. Streamlit abstracts away frontend complexity. You write Python code, and Streamlit automatically handles the web interface and interactions.

4. How do I run a Streamlit app?

You run a Streamlit app using the command streamlit run app.py. This starts a local server and opens the app in your web browser.

5. Can Streamlit apps be deployed online for free?

Yes. Streamlit provides a free Community Cloud where you can deploy apps directly from GitHub and share them with others via a public link.