Python in the browser

Why would anyone want to put Python in a browser?

• It's not JavaScript.
• We want Python everywhere.
• The web is a great portable UI toolkit.
• End-to-end form validation would be nice.
• Potential apps:
  • Distributed code review and version control (wiki)
  • Teaching tool
  • (Your idea here)
• Because we can. And because the web's important.

Technologies

• Crunchy
• Epiphany
• Jython
• Silverlight
• Adobe's mysterious technology
• Google App Engine
• TryPython.com
• PyPy
• JavaScripty stuff

Axis powers

Languages and libraries

• 
• Similar for Flash and JavaScript - less library support, but they behave like part of the browser.
• I'll be concentrating on Python-the-language parts only.

Crunchy

• http://crunchy.sourceforge.net/
• Crunchy is an HTML rewriting proxy, mainly intended as a teaching aid.
• It sits on your web server and rewrites pages before serving them.

• print "Hello, CamPUG, it's me, Crunchy!"
          

• If this page were being hosted via Crunchy, there would be an interpreter window there.
• The HTML source to put an interpreter in the page:

  <pre title="interpreter">
  print "Hello, CamPUG, it's me, Crunchy!"
  </pre>
          

• The source to launch the page in Crunchy:

  python crunchy.py --completely_trusted=talk.html
          

• ...but it doesn't work with this because this page uses JavaScript, which it doesn't trust, even with the "completely_trusted" url.
• It's paranoid about JavaScript because it can't run Python safely.

Epiphany's Python console

• Epiphany is the GNOME web browser (i.e. Linux/BSD only).
• It supports Python (or C) plugins in the same way that Firefox supports JavaScript plugins.
• It also has a Python console plugin, much like Firefox has Firebug for JavaScript.
• I've not played with it much.
• It's not really what we're looking for, since relatively few people use Epiphany, but it's still a good thing.
• Documentation on writing extensions:
  http://www.gnome.org/projects/epiphany/documentation/extensions/index.html

Jython

• Jython is massively under-used.
• It's brilliant for working/playing with and testing Java classes from a normal Python console as if they were Python objects.
• It works both ways, Java-in-Python and Python-in-Java.
• And it works in the browser.

Jython 2.5 is in alpha!

• Jython 2.5 alpha is now out!
• Important since Jython was previously languishing at 2.2, and is now basically on a par with normal Python.
• One problem. Jython 2.2 was 4.4MB. Jython 2.5a1 is 13.3MB.
• http://wiki.python.org/jython/JythonMonthly/Newsletters
• http://planet.jython.org/

Jython example

• This ships with Jython in the Demo/applet directory:

• from java import awt, applet
  
  class HelloApplet(applet.Applet):
      def paint(self, g):
  	g.setColor(awt.Color.black)
  	g.fill3DRect(5,5,590,100,0)
  	g.setFont(awt.Font('Arial', 0, 80))
  	g.setColor(awt.Color.blue)
  	g.drawString('Hello World', 90, 80)
  
  

• There isn't much documentation for this stuff, but ask me and I'll dig out what I've done to make it go.

Silverlight

• Get Silverlight 2.0 beta - "4MB download, 10s install"
• Get "Dynamic Silverlight" from DynamicSilverlight.net.
• See "Python in your browser with Silverlight" walkthrough docs
• App gallery, inc. DLRConsole Microsoft demo app - Python/Ruby/JS console
• Come to PyCon UK and hear Michael Foord describe it!
• www.TryPython.org, running "pythoninthebrowser":
• Python in the browser starting (requires Silverlight 2 Beta 2)...

Silverlight (SilverShell)

• SilverShell looks a bit prettier.
• 

• IronPython on Silverlight can talk to JavaScript.
• ...but developing for this platform without Visual Studio? Dunno.

Quake in the browser

Adobe's C++-to-Flash compiler

• This is all as-yet unreleased.
• But so far it looks like it works via:
C code --> llvm-gcc --> llvm --> Adobe VM (ActionScript) --> Tamarin bytecode
• Interview with the developer, Scott Petersen

Google App Engine: shell.appspot.com

• Executes on the server
• In a Google-proprietary Python sandbox
• There's an Apache-licensed sandbox for development, but it's not secure.

TryPython.com

• Executes on the server
• Needs to be run in a virtual machine sandbox (e.g. User-Mode Linux)
• With a read-only filesystem and firewalled out from all ports except 80.

Python in the browser?

• PyPy
  • PyPy has a JavaScript backend.
  • It doesn't work very well yet.
  • But it does work.
  • http://play1.codespeak.net:8058/
    
  • But PyPy is big and no-one understands it.

Python in the browser?

• A Python interpreter in JavaScript

HotRuby

• HotRuby - a Ruby interpreter in JavaScript
  • Uses Tamarin, Flash's virtual machine, donated to Mozilla
  • It's faster than Ruby on some benchmarks!
  • (That's because Ruby is sloooooow.)

Rumours of JavaScript's death...

• Greatly exaggerated I'm afraid.
• "a rushed little hack for Netscape 2 that was then frozen prematurely"
• On the upside, it's coming back as something actually good.
• "Stand on Python's shoulders"
• Features
  • Lambdas:

    function(x) x * x

  • Generator expressions:

    dict([s, [u for (u in unitlist) if (u.contains(s))]]
         for (s in squares))

• And very fast.
• And in Firefox 3 since last May.
• And Safari (WebKit) has just announced an even faster JavaScript engine, SquirrelFish.

Thank you.