Pymonkey is a Python C extension module to expose the Mozilla SpiderMonkey engine to Python.
Rationale and Goals:
Python and JS are fairly complementary languages. Python provides tremendous developer productivity via its dynamic language features, its vibrant library of third-party client-side code, and its ease of readability. JavaScript, on the other hand, is widely known by a vast number of casual programmers due to its availability in web browsers; it was also envisioned from its conception to be executed as untrusted code, which gives it a lot of security features that Python has always lacked.
There’s an increasing need for being able to run JS on the server side–particularly untrusted JS. For instance, being able to duplicate business logic on the server and client (i.e., browser) would be very useful. Standards-based solutions like ServerJS are currently paving the way in this field. There’s Java-based solutions like Rhino out there, but nothing really mature is available for the Python world. Ideally, Pymonkey should enable a Python programmer to create a custom sandboxed environment for executing JS code without needing to write any C.
Pymonkey should have awesome Sphinx documentation with doctests and all the trappings of a model Python package. Not only should it be easy for Python programmers to learn how to use the module, but it should also be easy for them to learn more about how SpiderMonkey works by reading the documentation and playing around with the code.
Pymonkey needs to have outstanding developer ergonomics. Full cross-language stack tracebacks should be available, for instance, and developers should be able to easily debug. Access to memory profiling facilities in JS-land is a must.
The module uses the Python C API: no SWIG, Pyrex, or other intermediaries. The obvious disadvantage here is that it means more C code, but the advantages are that
The module also doesn’t use ctypes because using the SpiderMonkey C API requires fairly complex preprocessor macros defined in the engine’s header files.
Finally, Atul has never really made a straight Python CAPI module before, so he wanted to give it a try.
You can either build SpiderMonkey off the mozilla-central HG repository, or off a mirror I made of its SpiderMonkey directory. The latter can be obtained here:
http://hg.toolness.com/spidermonkey/
Just HG clone that repository and read the instructions in the README to build SpiderMonkey.
Then come back to the root of your pymonkey repository and run:
python manage.py build --static --objdir=PATH_TO_OBJDIR
Where PATH_TO_OBJDIR is the path to your Mozilla/SpiderMonkey build’s objdir.
Note that at the moment, the build script is only tested on OS X.
There’s a number of challenges that need to be resolved before pymonkey can be really usable. Here’s some of them.
Garbage Collection
Python’s garbage collection uses reference counting, whereas SpiderMonkey’s is mark-and-sweep. We’ll likely run into situations where there are cycles that exist between SpiderMonkey and Python objects; this is actually quite similar to the relationship between XPCOM and JavaScript in the Mozilla platform–XPCOM uses reference counting too–so detecting such cycles will probably involve creating something akin to XPCOM’s cycle collector.