This Python module allows for the implementation of Javascript?
classes, objects and functions in Python, as well as the evaluation
and calling of Javascript scripts and functions. It borrows heavily
from Claes Jacobssen's Javascript Perl module, which in turn is
based on Mozilla's PerlConnect Perl binding.
This code was originally written by John J. Lee in 2003. After being unmaintained for a number of years, it was subsequently picked up by Atul Varma in 2008.
The first thing you'll want to do is create a Runtime instance,
which encapsulates a JSRuntime object from Spidermonkey. From the
JSAPI User Guide_:
A JSRuntime, or runtime, is the space in which the Javascript
variables, objects, scripts, and contexts used by your application
are allocated. Every JSContext and every object in an
application lives within a JSRuntime. They cannot travel to
other runtimes or be shared across runtimes. Most applications only
need one runtime.
Creating the Runtime instance is straightforward:
from spidermonkey import Runtime rt = Runtime()
You'll then want to use the Runtime to create a Context
instance, which encapsulates a JSContext object from Spidermonkey.
From the JSAPI User Guide:
A JSContext, or context, is like a little machine that can do
many things involving Javascript code and objects. It can compile
and execute scripts, get and set object properties, call Javascript
functions, convert Javascript data from one type to another, create
objects, and so on.
In Firefox, for instance, a different context is used for each webpage you view. A separate context is even created for each physical browser window, because much of Firefox's functionality is actually written in Javascript. Contexts can have their own security policies associated with them, and objects can be shared between multiple contexts.
Creating a context in Python-Spidermonkey is done like so:
cx = rt.new_context()
Now that you've got a context, you can do lots of things, like evaluating arbitrary Javascript expressions and using their results in Python code:
cx.eval_script("1 + 2") + 3 6
We can create classes in Python and access them in Javascript, too:
class Foo: ... def hello(self): ... print "Hello, Javascript world!" cx.bind_class(Foo, bind_constructor=True) cx.eval_script("var f = new Foo(); f.hello();") Hello, Javascript world!
We can also get back objects from Javascript and use them:
f = cx.eval_script("f;") f.hello() Hello, Javascript world!
.. _JSAPI User Guide: http://developer.mozilla.org/en/docs/JSAPI_User_Guide
The module currently has a number of features that still need to be implemented. For instance, it's not yet possible to call a function defined in Javascript:
cx.eval_script("function foo(x) { return x + 1; }; foo;") {'prototype': {}}
Errors in Javascript code also don't produce particularly helpful tracebacks:
cx.eval_script("3 + undefinedVariable") Traceback (most recent call last): ... JSError: can't evaluate Javascript script
Note that at present, installation has only been tested on OS X and 64-bit Ubuntu Linux; support for Windows is forthcoming.
At present, you'll need a C compiler on your system to install this
extension, as well as the Pyrex_ package.
Check out the Python-Spidermonkey module from the SVN repository_.
From the root of your checkout, run::
python setup.py build
Don't worry about the compiler warnings. Then, with appropriate permissions, run::
python setup.py install
.. Pyrex: http://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/
.. SVN repository: http://code.google.com/p/python-spidermonkey/source/checkout
The module has a test suite. Just run::
python test.py
Note that one of the tests currently prints out a Javascript error
message. This isn't a test failure (though it is a bug_).
.. _bug: http://code.google.com/p/python-spidermonkey/issues/detail?id=1
Thanks to Brendan Eich for help with several Spidermonkey issues (and
for all his Mozilla work), and to Erwin on the freenode #c IRC
channel for gdb tips.