RapydScript in a Nutshell

RapydScript Logo My last post mentioned RapydScript, a JavaScript variant with Pythonic syntax which I’ve come up with to speed up web-development. I haven’t had much free time to post since then, but I have been updating RapydScript this whole time. The bitbucket repository for the language started drawing some followers, and I am now getting questions in my inbox regarding plausibility of developing large-scale application in RapydScript. To address these concerns, and explain how to leverage RapydScript, I decided to write this post.

Before starting your project, it’s important to understand what RapydScript is and what it is not. RapydScript does not aim to emulate Python in JavaScript like most other Python-to-JS compilers such as Pyjamas, Pyjaco, and Skulpt. RapydScript to Python is what CoffeeScript is to Ruby (actually, RapydScript and Python have more in common). The point is, it’s important to understand that when writing RapydScript, you’re still using JavaScript. The code doesn’t get abstracted into a sandbox or wrapped in special types. This has a few advantages and disadvantages.


The main advantage of such approach is closer integration with JavaScript. Your code will load and run faster than similar code written for one of the other Python compilers (except PyvaScript, which will work just as fast). Additionally, your code doesn’t need hacks or wrappers to invoke or create native JavaScript and DOM objects, anything JavaScript has access to, RapydScript has access to. Drawing its power from JavaScript’s prototype, RapydScript’s class inheritance system is more intuitive than Python’s. RapydScript can create object literals (similar to C structs), create anonymous multi-line functions, and do some other goodies that pure Python can not. You can use $ in your variable names and use jQuery (or any other JS framework) without hacks. You can even debug your code by reading generated JavaScript that works and looks almost the same way as original code. Basically, RapydScript has all the advantages of native JavaScript. In fact, it’s very easy to debug RapydScript using Chrome’s Developer Tools or Firefox’s Firebug, other Pythonic solutions don’t have this benefit.

The other advantage is that while RapydScript does have a standard library, it does not rely on it to be usable. This means that even if I decide to abandon the project tomorrow for some reason, you will not be stuck with a half-functional solution for your front-end. Even with a limited subset of Python library implemented, RapydScript is 100% usable and capable of building large-scale web apps, because its main advantage isn’t in its standard library, but in cleaning up JavaScript syntax. In fact, you can forego RapydScript’s stdlib.js in your project altogether and replace it with underscore.js. You will also automatically benefit from new JavaScript features as they appear and can continue using the compiler regardless of how old it is.


The disadvantage of RapydScript (when compared to other Python-to-JS compilers, not counting PyvaScript) is also its close integration with JavaScript. RapydScript does not aim to catch errors JavaScript ignores. If you access an out-of-bounds cell in an array, you will get an undefined variable, not an IndexError (likewise, 1/0 is infinity). You can’t use negative indexes to traverse arrays in reverse (you can use negative indexes via list.__getitem__(), however). It turns out, however, that for properly written code, these disadvantages aren’t a problem. As long as you understand that the language is not pure Python, and the coding style a bit different, you will not have problems with RapydScript.

Why is it better than JavaScript?

If RapydScript has the same advantages and disadvantages as JavaScript, the question you might then have is “Why use it instead of JavaScript?”. The answer is “Because it brings many of the same benefits Python programmers already enjoy into JavaScript”. These benefits include all of the following and more:

  • Classes and Inheritance
  • Python Standard Library (only a portion of it is included so far, but more will be with time)
  • Clean, easy-to-read, Pythonic syntax
  • Better Variable Scoping (and Variable Shadowing)
  • Implicit Tuple Packing/Unpacking
  • Better Optional Argument Implementation
  • List comprehensions
  • Ability to import multiple modules into a single chunk of code (allowing easier code reuse)

If you spend a few minutes coding in RapydScript, or even checking out its examples, you will notice that once the ugly parts are removed from JavaScript, it’s actually a very beautiful language (allowing for code that is even cleaner than its Python-equivalent). And that’s exactly what RapydScript does, it cleans up the language so you can enjoy its true potential.

So who should use RapydScript?

The audience that will enjoy it the most is probably Python developers who want to write JavaScript code. There is a reason many Python companies choose to do their JavaScript development in CoffeeScript instead of using one of the existing Python-to-JavaScript compilers. The reason is performance, debugging ability, and integration with other JavaScript. RapydScript shares all of the advantages of CoffeeScript without introducing messy and confusing syntax.

RapydScript in Commercial Projects

I have no problem with people profiting from the code they write in RapydScript. Both, your code and the JavaScript you generate is yours to do whatever you want with. RapydScript itself is licensed under GPL, but all of its current libraries are covered by Apache license. This is to allow you to import those libraries into your project without being forced to open-source your entire front-end. I ask that other developers submitting new libraries for RapydScript also use a permissive license, but that is up to the developer.

This entry was posted in Languages and tagged by Alexander Tsepkov. Bookmark the permalink.

About Alexander Tsepkov

Founder and CEO of Pyjeon. He started out with C++, but switched to Python as his main programming language due to its clean syntax and productivity. He often uses other languages for his work as well, such as JavaScript, Perl, and RapydScript. His posts tend to cover user experience, design considerations, languages, web development, Linux environment, as well as challenges of running a start-up.

3 thoughts on “RapydScript in a Nutshell

  1. Do you mind if I quote a couple of your articles as long as I provide credit and sources back to your weblog? My blog is in the very same niche as yours and my users would certainly benefit from some of the information you present here. Please let me know if this alright with you. Thank you!

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>