However, the "icky legacy stuff" happens to include every program I've written in the last 5 years, as well as really important functionality like GTK bindings, database support, and compatibility with applications (like GIMP, Gaim and Blender) which embed Python themselves. so I need something more substantial to get excited about. Something to make it worth the rather onerous effort of upgrading the Twisted codebase, and simultaneously breaking support for millions of existing Python installations. Some of the "substantial" new features I've seen, like the new "iostack" library, seem to be controversial. I haven't done a thorough code review myself, but a few comments on the mailing list, like "8k is a perfect buffer size for any application", suggest that while there may be improvements, these changes are far from problem-free. (Not to mention the fact that a large portion of what iostack is trying to accomplish is the sort of thing that would be features in Twisted anyway, so it's likely we won't be using much of that code...)
PyPy brings some of this effort along with it as well, but PyPy's advantages are much clearer: it will be about a zillion times faster, it will make writing bindings to existing native functionality fundamentally easier, and it might be possible to add core language interpreter features, like restricted execution, without having to patch the core itself. Also, PyPy is currently targeting fundamentally the same language as Python 2.4, whereas Python 3000 is intentionally incompatible, so it will be possible to support Python 2.4 and PyPy, although PyPy may require a lot of conditional blocks to work right in the real world.
This is all a high-level understanding gathered from listening to rumors, perusing mailing list archives, reading a few websites, and attempting to read between the lines. I could be wrong about both projects. With my current understanding though, the plan for the Twisted project is to support the 2.x Python series and PyPy as soon as it's feasible, but ignore Py3k until there is a compatibility layer which would allow us to migrate gradually rather than in one fell swoop.
Lots of Python fans seem to read this blog, so maybe you can help me out. What new features or idioms should I be really excited about in Python 3000? Am I missing something fundamental about what it's trying to achieve?
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