DjangoOnJython

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Summary of Django on Jython: The Gaps

The most important thing to know about Django on Jython is that we are almost there, and with clean code. End-to-end functionality is demonstrated by the admin tool running in full CRUD, along with more than 90% of successful tests.

Moreover, we are part of the goals for the upcoming Django 1.0 release.

Running on Jython

To run Django on Jython, with a PostgreSQL backend, the easiest way to get started is to follow the instructions outlined [http://blog.leosoto.com/2008/07/my-new-djangojython-developer-workflow.html here]. If you prefer you can manually get Jython asm branch and Django trunk to later apply the patches at https://hg.leosoto.com/django.patches/file and https://hg.leosoto.com/jython.patches/file

Additionaly, you will need the [http://code.google.com/p/django-jython django-jython integration code] which contains the JDBC database backends and some management utilities.

Status

This is mostly outdated. We are working on updated status and documentation. Sorry for the inconveniences.

Here's what works:

syncdb and the very cool Django admin run; many unit tests pass. You can run with internationalization enabled. You do need to run the dev server with --noreload for now. We need to document here how to run with [http://www.xhaus.com/modjy/ modjy], which is Alan Kennedy's servlet container for WSGI apps.

In running the model unit tests, here are the things we seem to be missing:

• We still have some encoding problems, again seen in doctests. An example where output is expected to be lower case hex, not upper case. I fixed the problem in PyUnicode, but there are more places. Our current plan is to make test_unicode.py pass (accounting for any UTF-16 vs UCS-2/UCS-4 issues).

• Problem with the ManagerDescriptor handling, in django.db.models.manager.

• No decorators yet! (But they are coming soon, and are now available experimentally for Jython.)

There may be some other rough categories, we need to look at the failures more systematically.

[http://dojstatus.leosoto.com Here are some unofficial test suite results]

Next Steps

On the Django front, get more of the unit tests running!

Modern is now in trunk.

Historical Notes

(Preserved to show how much we had to go through...)

Merging Modern into trunk

With the Modern branch was recently merged in (and deleted), we have consolidated the bugs, workarounds, and patches found below -- plus a bunch more. The most important aspect is that we have tried to make Jython conform more to CPython, using Django as our guide, although there are some gaps - especially if Django already had incorporated fixes. Our driving goal is to converge on these gaps over time. Please note that is intended to be stable, performant code, and so far that looks to be the case!

Here are some of the things we addressed:

• The test_extcall unit test still fails. This appears to be a dependency on dict traversal being a specific arbitrary order different from CPython's. Google's GHOP produced an improved version for Python 2.6, so we will look at this as a starting point for further analysis.

• Tristan King provided a near complete subset of the functionality for time.strptime, as implemented in org.python.modules.time.Time. This needs to be enhanced. All unit tests in the CPythonLib version of test_time now pass except for strptime -- specifically the conversion specifier '%c' -- so we can also move to that, and discard our Jython version, when this is completed. That should be soon! Done, and in trunk.

• Decide whether we should use ConcurentHashMap or not as the backing hash map for dict and __dict__. CHM introduces creation overhead, but it should prove to be far more scalable on multicore systems. The programming model is also far nicer with respect to Jython. Done.

Former Major Problems

• Many doctests are fragile, because they depend on the dict traversal ordering; in Jython, this is different that CPython, and if we adopt ConcurrentHashMap, it's not even repeatable. This would seem to be a pervasive bug in Django. This was fixed on Django.

• Jython does not support non-str keys in __dict__ right now. Jim Baker replaced the custom dictionary in PyStringMap with a HashMap (along Groves' earlier work). This change should resolve this problem. Try the [https://jython.svn.sourceforge.net/svnroot/jython/branches/modern/ modern] branch. Problem encountered in django/utils/_threading_local.py.

• Something goes wrong with re.compile(u"([\u0080-\uffff])") in django/utils/text.py I think it is a lacking in our array implementation but this needs more investigation.

  • See [http://sourceforge.net/tracker/index.php?func=detail&aid=1544953&group_id=12867&atid=112867 bug 1544953]

• django/views/debug.py wants to know a function's __module__. functions don't have a __module__ attribute in jython yet. [http://sourceforge.net/tracker/index.php?func=detail&aid=1800472&group_id=12867&atid=312867 patch]

• inspect.getargs() doesn't work.

  • That's because co_code isn't supported by PyTableCode.

    • But, co_code is used by getargs() only to discover anonymous tuple arguments. Commenting such section seems to be enough to get the other cases working.

    • workaround [https://dev.archer.edu.au/projects/kepler/svn/jython-django/trunk/jython-patches/co_code-workaround.patch patch]. just sets co_code = "". i haven't come across any problems for this inside django yet, but i'm sure it'll break other python code -- TristanKing

• time module lacks strptime().

  • workaround [https://dev.archer.edu.au/projects/kepler/svn/jython-django/trunk/jython-patches/time-strptime.patch patch]. this is incomplete, untested, and not optimal but works for the django tutorial -- TristanKing

• inspect.isclass(time) shouldn't return True [http://sourceforge.net/tracker/index.php?func=detail&aid=1786009&group_id=12867&atid=112867 bug]

  • Django [http://code.djangoproject.com/changeset/6194 works around this] until it's fixed.

Former Minor annoyances

• slice should be a type, not a function. [http://bugs.jython.org/issue1791931 bug] [http://bugs.jython.org/issue1798544 patch]

• PyBoolean.__tojava__ returns an Integer

  • It affects zxJDBC unless a DataHandler sets the right type of boolean parameters. Fortunately, JDBC30DataHandler does this thing, at least on my limited tests -- LeonardoSoto

• Jython does not have __builtins__ as a module. Django adds "_" as a convenience method for calling gettext in django/conf/__init__.py.

  • According to the Python docs, __builtins__ is a implementation detail and shouldn't be used by portable applications, so it's a Django problem. (See note about __builtins__ here: http://docs.python.org/ref/naming.html)

• Jython methods are not descriptors. It seems a implementation detail. [http://code.djangoproject.com/ticket/5664 django patch]

• Jython classes which extend dict cannot be compared to a dict. [http://bugs.jython.org/issue1804011 bug] [https://dev.archer.edu.au/projects/kepler/changeset/149?format=diff&new=149 django patch]

• Jython doesn't recognize __unicode__ methods assigned to instances.

  • But, this is the only __*__ method where CPython allows this, and it's not documented anywhere. So, it's a implementation detail and should be fixed on Django. [http://code.djangoproject.com/ticket/5560 django patch]

Already Fixed

(And many more!)

• Jython does not have sys.stdout.isatty. Jython should get added to the exclusions around that call in django/core/management.py (win32 and 'Pocket PC' are already excluded).

  • Fixed in [http://code.djangoproject.com/changeset/6032 Django changeset 6032]

• stringmap (or the __dict__ implementation) needs a pop(o) method.

• Jython lists and tuples don't have __iter__ .

  • Fixed in [http://code.djangoproject.com/changeset/6211 Django changeset 6211]

• Jython does not have os.getpid().

  • Django workarounds it now.

• Jython does not have os.W_OK needed in django/core/management.py. This probably will not be hard to add this since java.io.File has a canWrite().

  • os.chmod should be implemented too (After checking for write permissions, Django will try to change them if necessary).

    • That's hard. Maybe Django shouldn't check for permissions if running on Jython.
  • Django don't check or change file permissions when running on Jython now

• The U (Universal newlines) flag for open() isn't recognized on Jython

• Unicode string interpolation doesn't work

• object has a __unicode__ attribute (it doesn't on CPython) [http://bugs.jython.org/issue1800378 bug] [http://bugs.jython.org/issue1800381 patch] -- TristanKing

• metaclasses need to know the __module__ of its classes [http://bugs.jython.org/issue1781500 bug] [http://bugs.jython.org/issue1789137 patch]