Hacker News Reader

Comment by factorialboy | Hacker News Reader

Would love to learn how Brython completes with Transcrypt (https://www.transcrypt.org/) and PyJs (http://pyjs.org/)

Is there a page for that?

'pansa2 already linked this upthread, but a colleague of mine wrote an in-depth comparison of six popular Python-in-the-browser implementations, and their trade-offs (with sample code). It's a writeup from a PyCon UK talk: https://anvil.works/blog/python-in-the-browser-talk

Brython feels like a Python interpreter (it's actually transpiling to javascript with a thin compatibility layer, cf. https://github.com/brython-dev/brython/wiki/How%20Brython%20...), you can use Python live in the browser, while Transcrypt transpile Python (or nearly Python, depending on what features you activate) to Javascript ahead of time (this can be achieved with Brython CLI too).

Brython has a better compatibility, but Transcrypt being pure javascript on the browser should be faster (I didn't made the comparison myself though). Both projects are complementary.

PyJS is a hostile fork (or I should say "hijack", but that's a long story) of Pyjamas, a Python 2 to Javascript compiler. I'm not sure where they are now, but at the time Pyjamas was Python 2 only and there was no plan to move it to Python 3 as this would mean a full rewrite of the transpiler.

It's pretty similar to Transcrypt except that it comes with a library which is a rewrite of GWT for Python. With that you end up writing web application in a similar way as you would do for desktop application. I've been using Pyjamas for years, it was working quite well (but you had to get used to some bugs/incompatibilities with Python, and I have not experienced that with Brython so far). About the library, while it seemed like a neat idea at the beginning, at the end it was an experience too distant from web developing, and meanwhile HTML and CSS improved a lot so it doesn't really makes sense anymore.

So from my experience :

- you want real Python 3 and being able to use it dynamically (in a live console for instance) ==> Brython

- you want something as fast as javascript with clean syntax of Python ==> Transcrypt

Both work well with JS libraries, Brython in addition re-implement most of Python standard API (but it's long to import, so it's often better to use JS libraries or native methods).

In addition, and really subjectively, I find the Brython community really nice, the main developer is reactive and kind.

Brython gives you real Python traceback, and you can even run pdb inside the browser (which will block your scripts) or an Inspector (a non blocking Python console) allowing to transfer objects between Python and Javascript for inspection in dev tools.

edit: corrected the initial statement, Brython feels like an interpreter, but it's actually transpiling, so you don't have such a big performance impact.

edit2: added that Brython can be compiled AOT from CLI too + precisions that I didn't compared with Transcrypt myself

I've been using Transcrypt for the last few months and am impressed at how well it integrates with JS libraries. But then that was done with intention in the design. I've been writing React+MaterialUI apps in Python and the resulting code actually still looks like the Python I know and love. I did get pulled into the NPM/Parcel world for JS package management & minification, but the build step is relatively painless and Transcrypt has a Parcel bundler plug-in so there's no extra work involved to use it.

The fact that Transcrypt hasn't implemented the full standard library yet hasn't been much of an issue for me so far either. In the very few cases where I was missing something, I just pulled in a JS library in it's place (i.e. deepcopy).

While using Transcrypt this way requires you to understand the APIs of the JS libraries that you use, the code you actually write is 99% pure Python.

just a correction for my comment above, I should have written "Brython feels like a Python interpreter", but it's transpiling to JS too, the difference is that it's done directly in the browser (it's also possible ahead of time from CLI), and then the JS is stored in indexecDB (this can probably be compared to .pyc from CPython).

It's explained there for the curious: https://github.com/brython-dev/brython/wiki/How%20Brython%20...

edit: I've updated initial comment.

I hadn't heard of Transcrypt, looks neat. Can it be used server-side? Leveraging a JavaScript JIT seems like a good way of 'passing the buck' for getting high performance out of a dynamically typed language.

https://stromberg.dnsalias.org/~strombrg/pybrowser/python-br...

https://yasoob.me/2019/05/22/running-python-in-the-browser/

Reply on news.ycombinator.com