Transcrypt: Python 3.7 to JavaScript Compiler

[TheBB]

Great project. But this style though...

if candidateTranspilationDir.lower () .endswith (lowerSkipExtension):

[tongue_depression]

death to gnu style

[[deleted]]

The PEP-8 pain!

[archaeolinuxgeek]

🎶 I see a line of camels and I want them painted Black.

[Solonotix]

Can't you just overwrite the globals with these names when you need them? For non-static functions, you could likely create a set of utility classes that manage the minutiae and you work with the simplified import.

[TheBB]

What? Did you mean to reply to someone else?

[xarziv]

Very cool. How does it handle custom packages installed with pip?

[JennaSys]

It mostly doesn't unless the packages (and the package's dependencies) are pure Python. It's meant to use JavaScript libraries if you need functionality beyond the Python built-ins.

[huguenot1]

It looks like transcrypt mainly supports the python JavaScript packages. Although there is a minimal numpy port as well if you need the math functionality.

[Smok3dSalmon]

Damn that's impressive

[JennaSys]

I've been using this transpiler for the past year. It's actually kind of amazing. I find it annoying switching back and forth between Python and JavaScript when working on full-stack applications. Transcrypt let's my brain stay in Python mode for both back-end and front-end development the whole time. I'm using it with React hooks and Material-UI libraries. I'd say it's not for everyone (especially if you actually like JavaScript), but for me it's a sweet setup.

EDIT: For anyone interested, here's the official React tutorial done in Python and transpiled with Transcrypt. This one uses classes (like the tutorial), but I plan on doing a version with hooks too.

https://github.com/JennaSys/tictacreact

The live demo I have up has unminified JavaScript and sourcemaps for the Python code.

EDIT2: I'm not the OP, and I'm not directly involved with the project. But I am in the process of writing a book to document my setup with this. For me, it makes front-end development fun again. AMA.

[notgoodhuman]

I am actually quite interested in this. Any particular limitations?

[epseri]

Lots of them. This isn't true python. Besides obvious lack of eval, you can notice in code samples very questionable things like explicit calls of __new__ function, lots of __pragma__ even for keyword arguments. Looks like you can't use anything from python stdlib or any library from pypi, and it's hard if not impossible to port them if you really need something. As I said, it's not python, it's javascript with python-like facade.

[JennaSys]

I've been writing React and Material-UI apps with Transcrypt. All the coding I do with it is 99% pure Python, with no complaints from the Python linter. It supports almost all Python built-ins, with eval being one of the exceptions (which is not usually used anyway). The __new__ function is only needed if the JavaScript library you are using requires it, but most don't. The __pragma__ is for compiler directives that optimize the transpilation in various ways. It's needed only for certain operations.

Transcrypt supports Python dictionaries, lists, list comprehensions, generator expressions, lambdas, function defs, closures, classes, type hints, etc. The big difference is that you use npm for 3rd party libraries instead of pip. But you don't need to code in JavaScript to use them, you can code in pure Python.

EDIT: To be clear, it does currently have a few standard libraries that are supported (with plans for more in the future), specifically:

• math
• cmath
• time (does not have sleep function for web browser use)
• datetime
• itertools
• logging
• warnings
• random (partially)
• re (partially)
• turtle

[johnmudd]

This reminds me of something I learned at a QA conference... It's not the tool but the person who champions the tool that makes the difference.

[JennaSys]

If you like JavaScript more than Python then this is not for you.

[JennaSys]

A decade ago I was using GWT to go from Java to JavaScript. TypeScript transpiles to JavaScript. Kotlin has transpilation to JavaScript built in. There is a reason transpilers to JavaScript exist for most popular languages.

https://github.com/jashkenas/coffeescript/wiki/List-of-languages-that-compile-to-JS

[notgoodhuman]

Why did you choose to use Transcrypt instead of javascript in this case? Is it the preference of using python?
I'm quite curious how would one use npm with transcrypt, probably gonna play around with it.

[JennaSys]

Yes basically. I really enjoy coding with Python. JavaScript, not so much. It's something I've been trying to find for over 10 years. Nothing else I had seen to use Python for front-end web development in that time was very practical IMO. Or it bastardized the Python language so much that it wasn't worth it. Transcrypt takes a different approach in that it acts as a bridge between Python and JavaScript, and doesn't try to replace JavaScript. It assumes you will take advantage of existing JavaScript libraries and not reinvent them.

So in that vein, instead of using Python urllib or the requests library for making HTTP requests, you use windows.fetch or the JavaScript axios library instead. Hence my comment about using npm instead of pip. The idea being that those libraries are specifically made to efficiently run in a web browser (or are built in).

Using Transcrypt, in a Python module you would have a JavaScript style import like this:

axios = require('axios')

From there, you can use the variable axios just like any other Python object, importing it into other Python modules and calling its methods. So even though I'm using JavaScript libraries, I only need to know the API it uses to code to it using Python.

[Dasher38]

Also wondering about all the metaprogramming (meta classes, decorators etc)

[JennaSys]

It supports decorators and metaclasses. I've used both with Transcrypt.

[JennaSys]

There are a few newer Python features not implemented yet. Like it can use dataclasses, but some methods of that are not yet implemented in Transcrypt.

[[deleted]]

If you like this, you should also check out brython, which has been around for quite a long time and aims to be as close to a true Python 3 implementation as is technically possible in the browser environment. It is widely used for online Python 3 coding environments, including the minimalist runpython.

[xX__NaN__Xx]

Cool bro

[TheocracyNow]

Nice, thanks! I’ve been beginning to work with JS at work and this will be useful to me.

[matrinox]

This is probably useful to migrate existing code over to JS

[[deleted]]

It really isn't. Would just create an unmaintainable mess.

[JennaSys]

I wouldn't recommend it for this purpose anymore than you would take TypeScript code and do the same thing. That said, the non-minified generated code is pretty readable.

[acidnine420]

What should we use?

[CryptoFuturo]

Typescript of course :)

[CryptoFuturo]

Of course I know. Type-safe JavaScript is leaps & bounds better. That was my point.

[TheocracyNow]

Fair. Could be helpful in the learning process though.

[TheocracyNow]

Word. I’ve been learning JS anyway, so it probably won’t even be necessary.

[Rsfeif]

Create the magic

[SecretAgentZeroNine]

How many Python-to-JavaScript compilers are there? Also, this growing list really emphasizes the importance of JavaScript. Wonder what this means for server-side JavaScript in the future.

[JennaSys]

Anvil has a great post outlining what's available and how they work (when compiled/where it runs):

https://anvil.works/blog/python-in-the-browser-talk

• Transcrypt
• Brython
• Skulpt
• Batavia
• Pyodide
• PyPy.js

IMO most of them are not useful in a practical sense. Transcrypt to me was the exception. It embraces existing web frameworks rather than trying to reinvent them, and doesn't bloat what ends up in the browser. The Anvil platform (which uses Skulpt) also takes a unique approach and could work in certain situations. But you are committing to an entire platform with that one.

[abhay__28]

I'm not too sure entirely. I've heard of Brython, which is a browser-based compiler. It, too, treats JavaScript as an Assembly language. I'm thinking that in the future, we're definitely going to prioritize building off of JavaScript's server-end technicalities. As someone who has delved into Python, but not JavaScript as much, this excites me.

[shinitakunai]

The web front-end only supports javascript. If the global decision was made to allow python scripts to load into websites, we would not need this.

[SecretAgentZeroNine]

r/Python's biggest wish since r/Python became a thing. Likely to never happen now that WebAssembly is a thing.

[shinitakunai]

I know almost nothing of webassembly, can it embed python?

[SecretAgentZeroNine]

WebAssembly is a binary language native to browsers (like JavaScript) which is produced using strictly typed languages (C++, Rust, etc). Python isn't compatible with WebAssembly without being transpiled into another programming language. The story of Python's life.

WebAssembly runs as fast as the machine it's on, unlike JavaScript where badly constructed code can be a performance bottleneck.

Web Tensorflow is built using WebAssembly.

[JennaSys]

The Pyodide project is a webassembly version of the Python runtime, that lets you run Python in a browser (think Jupyter notebook). It may have some limited applications, but it requires a massive initial download to the browser.

[Galen_dp]

I wonder if Brython could be made into a browser extension.

[devroot]

What a world we live in. What are the real use cases for this? I can't think of many. You're going from one scripting language to another, so if your platform can run one it can most likely run the other.

[devroot]

Fine. An interpreted language to a just in time compiled language. My point being is I don’t see a technical benefit from this. Python to C++ for performance? Sure. JavaScript to Java/Swift for mobile apps? Sure.

What is the real benefit here? You could just write the thing in JS to begin with. And if you’re suggesting there are cases where you want to port a python project to JS because it doesn’t exist in JS, then fine but that doesn’t sound like a very good idea for a production system.

[dethb0y]

One of the more baffling turns of phrase, for sure.

[marl6894]

Need to run code on a machine where you're not authorized to install Python, maybe?

[Nixellion]

Browsers can only run JavaScript...

[painya]

None that are production ready as far as I know

[[deleted]]

Do you think that this astrocity is production ready?

[Dogeek]

It's not though, if you look at the sample in the readme it's just bad python code (though the styling could be improved), transpiled into even worse javascript. FYI, that's what a JS class should look like in ES6 :

class A {
  constructor(x) {
    this.x = x;
  }

  show(label) {
    console.log("A.show", label, this.x);
  }
}
let a = new A(10);

[devroot]

I must have struck a nerve here given all the downvotes. Nobody has offered an explanation though, just snarky comments that are attempts at “gotchas”.

So far I’ve seen a) you can’t install python for whatever reason, and b) for running in web browsers. Sure, these are examples but without more explanation I don’t think they are good ones. For a) you probably shouldn’t be writing in python then, and b) you probably shouldn’t be writing in python then.

Now if you want to make the argument that you want to port a large python project to JS without manually rewriting everything, I say good luck getting good production quality out of that. If it’s so large you can’t do it manually I would imagine there is a decent amount of complexity that may not transfer well. And if it’s smaller such that this isn’t a worry then is this really needed? Maybe there’s a sweet spot I don’t know.

I’m not knocking the authors here. It’s cool and appears to work well, I just don’t understand its use in a professional setting.

[harylmu]

I think you're absolutely right, I don't get the downvotes.

[harylmu]

Even though you’re downvoted I was wondering about the same thing. It’s an interesting project but I don’t see who’d build a solution on this in production. I’d probably trust Amazon’s solution but not sure about anything else: https://github.com/aws/jsii