Browser-based data apps with Pyodide and Preswald
Why running Python in the browser changes everything
Analytics has typically always been tied to local machines, servers, or cloud environments. You set up dependencies, install Python packages, and run your code in Jupyter, VS Code, or a terminal. That’s just how it works. But now, something very cool is now possible: you can run Python directly in the browser with Pyodide.
This makes sharing code easier, and opens up new ways to build interactive, web-based data apps. If you’ve ever struggled with setting up environments or explaining to someone why their version of NumPy doesn’t match yours, Pyodide solves that in one step: just open a URL, and everything runs in the browser.
🐵 Try it out today on https://github.com/StructuredLabs/preswald
Why pyodide is cool
1. No install, no setup.. it just works
Setting up Python environments is a pain. Whether it’s package conflicts, dependency hell, or just getting someone to install Python in the first place, it’s a blocker. Pyodide removes all that. Since it runs in WebAssembly inside the browser, you don’t install anything. Just load a webpage, and it’s ready to go.
2. Easy sharing and collaboration
Analytics is collaborative. But sharing code usually means sharing notebooks, dealing with dependency mismatches, or setting up cloud environments. With Pyodide, you just send a link, and the other person runs your code instantly. This makes it perfect for education, research, and interactive demos.
3. Works everywhere
Since it runs in the browser, Pyodide works on any device: laptops, tablets, even phones. It’s also offline-friendly because browsers cache the code, making it more reliable than cloud solutions that require an internet connection.
How pyodide actually works
Pyodide is a WebAssembly build of CPython. That means it compiles Python (and its core scientific libraries like NumPy, Pandas, and SciPy) into a format that runs inside the browser. It also has a bridge between Python and JavaScript, so you can call web APIs, interact with the DOM, or integrate with JavaScript-based tools like D3.js for visualization.
This means you can:
Run Python code in the browser without a backend.
Use scientific libraries without worrying about installation.
Build interactive, self-contained tools that work in any browser.
Too good to be true?
Pyodide is great, but it’s not a magic bullet. There are trade-offs:
Performance overhead. WebAssembly is fast, but not as fast as native execution. Pyodide is fine for most analysis, but heavy workloads are still better off running on a real machine.
Limited file system access. Since it runs in a sandbox, handling large local datasets is tricky. You’ll need to work with browser-based storage solutions.
No native threading. Python’s Global Interpreter Lock is already a bottleneck, and WebAssembly doesn’t fully support multithreading yet. Parallel processing is limited.
The Bigger Picture
Pyodide represents a shift in how we think about data apps. Instead of installing Python environments, we can run everything in the browser. Instead of worrying about dependencies, we can share code with a link. Instead of keeping computation locked to local machines, we can integrate it seamlessly with web applications.
This is just the beginning. As WebAssembly and browser APIs evolve, running Python in the browser will get even better.
🐵 Try it out today on https://github.com/StructuredLabs/preswald
Excellent post!