Realizing Jython 2.5

June 20, 2008 at 09:43 PM | categories: Jython, 2.5.x | View Comments

Jython 2.5 is really, finally, unbelievably coming together. This is the next release of Jython, after last summer's 2.2. In a nutshell, we have completed all new language features using an Antlr parser, except for absolute imports. All bytecode generation work, now using an ASM backend, is done. Of course, there are many outstanding bugs. And Python is not just a core language; we need to support fully the fact that "batteries are included". But let's look at where we are. Through the prism of what's new in 2.3, 2.4, and 2.5, here's what working:

  • 2.3: sets (PEP 218), generators (255), source code encoding (263), universal newline (278), enumerate (279), logging (282), Boolean (285), distutils (301), new import hooks (302), pickle enhancements (307), extended slices, datetimes, optparse. Still to go: csv, removing a dictionary in builtin that ensures that interned strings don't get in GC'ed (pre-2.3 behavior!, it helps to read what's new). Also various string, Unicode, and regex changes are mostly done in a separate utf16 branch that I'm currently in the midst of merging against trunk.
  • 2.4: unifying long integers (237), generator expressions (289), string.Template (292, but also needs new utf16 work), decorators (318), reverse iteration (322), subprocess module (324), multi-line imports (328), removal of OverflowWarning, min & max with keyword support, sorted. But we still need partial import with sys.modules, and I'm sure some more stuff I forgot. Decimal and -m support are working in student branches, we just need to incorporate.
  • 2.5: conditional expressions (308), partial functional (309, but we're cheating with a pure-Python version), distutils metadata (314), unified try/except/finally (341), coroutines and other generator functionality (342), with-statement, including contextlib (343), any, all. But we haven't done the exceptions remapping to new-style classes, absolute and relative imports, or all of the context manager support, such as in file. ctypes was a proposed Google Summer of Code project, but apparently PyPy has some work that's 95% the way there; we will talk with them at EuroPython. We need to look into what is necessary to make ElementTree work. sqlite3 depends on ctypes. As I was writing this, I tried out wsgiref; it works and I just committed it to the asm branch. (At some point, we will repoint everything like this to CPythonLib, but for now we are mixing it up as we go. Bear with us!)

Even quit() and exit() now work; I don't know when these oh-so-major features were added. We even now support large string constants. And of course, who can forget our support for the GIL (global interpreter lock) in Jython, something that Tobias Ivarsson, my Google Summer of Code student who is now working on an advanced compiler, added to __future__ as an Easter egg:

>>> from __future__ import GIL
Traceback (most recent call last):
  (no code object) at line 0
  File "<stdin>", line 0
SyntaxError: Never going to happen!

I would imagine that's definitive, we go against Java's native threads and compile to Java bytecode. It would be hard to have a GIL, even if we wanted one.

However, we are just turning the corner. The The Antlr parser in the asm branch currently does not support partial parses, and this breaks not only interactive sessions but doctests. Until this is solved - and Frank Wierzbicki is working like mad on this - we can't merge this branch onto trunk. But that should happen very soon.

With few exceptions, we simply go against the standard Python unit tests. Straightforward, cunning, or devious, we have labored against these unit tests. And in others, we have used Python as our foil: we support the same 2.5 AST parse tree, and we know this by comparing our parses with CPython's for all of the standard library - including those unit tests.

There's a lot more going on. I can't say enough about the work done by Charlie Groves, Philip Jenvey, Alan Kennedy, Nicholas Riley, and others to make this happen. Leo Soto, my other GSoC student, is making amazing progress on supporting Django on Jython, while finding and fixing bugs in Jython itself. Supporting Django forces us to find those gaps in compatibility. Similar efforts are going on with Pylons, TurboGears 2 (Ariane Paola, GSoC), and Zope (Georgy Berdyshev, GSoC). I'm also working on greenlet/Stackless support and involved in a collaboration with Jeremy Siek and Joe Angell at the University of Colorado to add gradual typing] (yes types! but only when you want to) to Jython. We have a T2000 contributed by Sun to let us see how much concurrency - in this case 32 hardware threads, 64 GB of memory - Jython can take advantage of. And so on.

Back to work!

Updates - 2008-06-24: we have support for new-style exceptions, the parser is now usable (but there are a couple of bugs left there), and Unicode support has been updated to UTF-16. See this posting, Flipping the 2.5 Bit for Jython.

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Django on Jython - Minding the Gap

January 03, 2008 at 09:59 PM | categories: Jython, 2.5.x | View Comments

Summary

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 a substantial number of unit tests and syncdb. But this has been achieved by so far requiring only 6 lines of code in changes to Django trunk. (There will be more, however, see below.)

Running on Jython

To run Django on Jython, with a PostgreSQL backend, the following steps are necessary:

  • Use the Modern branch of Jython. This consolidated the bugs, workarounds, and patches of numerous people -- plus a bunch more -- in a stable, almost-ready-to-be-merged-into-trunk version of Jython. 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.
  • Use the Django trunk (tested with rev 6992, later should be OK too).
  • Apply these two patches, django.dispatch.robustapply (diff) and django.views.debug (diff) due to Leo Soto. I would imagine these will be in Django trunk soon.
  • Copy these three files from CPythonLib to Lib: gettext.py, locale.py, optparse.py. Please note that these files are only partially working on Jython, that's why they haven't been promoted yet (gettext.py actually works, as verified by test_gettext.py, but depends on still failing locale.py). But they are very close, and they appear to be fine for Django. Certainly fine for this round of development!
  • Use the database backend zxjdbc_postgresql, which was contributed by Leo Soto. Frank Wierzbicki has an experimental backend for MySQL, this should be incorporated soon.

Status

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 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, accounting for most of the approximately 75 failures:

  • 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.
  • 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.
  • 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 in the newcompiler work I have been leading.)

There may be some other rough categories, we need to look at the failures more systematically. All that doctest noise is certainly annoying!

Next Steps

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

Before we can push modern into trunk, the following needs to be done:

  • The test_extcall unit test currently fails. This appears to be a dependency on dict traversal being repeatable, a bad assumption. However, it's a mind bending test. The 2.3 version is particularly problematic because it's not modular at all. Google's GHOP has just produced an improved version for Python 2.6 - we will look at this as a starting point.
  • 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. I just tested this, and 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!
  • 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.

Updates - 2008-06-24: I should have put this up a while ago, but Django on Jython is becoming a reality. Most importantly, Leo Soto is working with me through the Google Summer of Code on this project. The modern branch was merged into a trunk earlier this year, and has since been retired. CHM in fact has the right semantics, something I may discuss at a future point. Django has redone the doctest dict literals that were causing problems, and Leo provided a general solution when used with XML/XHTML.

Updates - 2010-09-13: Django on Jython is a standard PyPI project. The best reference for it can be found in our Jython book. Jython 2.5.2 is about out. The previous release fixed pretty much all of the other issues. And using ConcurrentHashMap has been a very good decision!

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