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Porting an existing Python module written in C into Java that Jython understands is a pretty straightforward task so it can serve as a good introduction to the Jython codebase. I'm going to explain how to go about porting the [http://www.python.org/doc/2.3.5/lib/module-csv.html csv] module here.
- Declare your intention to implement the csv module on the Jython dev list so no one else starts working on it.
- Add a new class org.python.modules._csv.java in src to mirror _csv.c from CPython.
- Add "_csv" to the builtinModules array in org.python.modules.Setup
- Run dist/Lib/test/test_csv.py. Everything will fail since none of the csv methods are implemented yet. Now pick one of the simpler tests and start adding methods to csv to get it to work. _csv.java will be an implementation of the stuff in _csv.c from Python. All of csv_methods from _csv.c needs to be implemented as static methods in _csv.java. You can get an idea of how it's done from _codecs.java and _codecs.c or any of the module implementations in org.python.modules and their corresponding C implementation. As you add the methods to _csv.java, Jython will pick up on them and parts of the tests will start working.
- Keep adding pieces to _csv.java till the tests pass
Submit a patch to the [http://www.jython.org/patches tracker].
- Revel in the glory of another implemented module
The table below contains modules implemented in C in Python that are missing in Jython. Feel free to grab one of them and get started. If none of them catch your fancy, run dist/Lib/test/regrtest.py. All of the skipped tests are for modules that are present in CPython but not in Jython, so they're fair game too. See the "Missing Modules" section of ../RegressionTestNotes for a list as of 20061123.
Module |
Taken |
Affected tests |
csv |
Y |
test_csv |
tarfile |
N |
test_tarfile |
unicodedata |
Y |
test_unicodedata,test_codeccallback |
heapq |
N |
test_heapq |
mmap |
Y |
test_mmap |
Comments
Why have you called the Java file _csv.java instead of just csv.java? Is there a convention here and if so, why don't all the classes follow the same convention.
pdrummond: Short answer: It's called _csv because that is what it's called in CPython!
Long answer: Hmmm. Will have to swat up on CPython's module naming conventions to answer this properly! I think CPython's general convention is "<name>module.c" so csv really should be "csvmodule.c" shouldn't it? I guess the underscore is necessary because there is a csv.py wrapper so the "csv" name is already taken, but I need to check this to be sure!
FrankWierzbicki: This is actually a CPython convention -- but one that is inconsistently applied -- the 2.6 version is making this more consistent. The convention is: for a given module x, there is usually an implementation in python called x.py and a c implementation called _x.c. Generally x.py tries to import _x.c at the beginning -- this way implementations like Jython can get a pure python implementation right away, but can also implement a faster version that we should call _x.java later. I'd like to add that I would recommend looking at the CPython implementation as you go -- there are almost always subtleties that the tests miss - I used to assume the tests where good enough but got burned a couple of times this way.
Will the test_csv.py file automatically appear after a build or do we have to implement this ourself?
pdrummond: test_csv.py will appear auto-magically after a build in dist/Lib/test (at least, it will in the 2.3 branch) and it is a CPython test script.