PyPy and Jython may lag behind, but that's not a huge problem. I would love to use dict comprehensions and {} sets like I can in CPython 2.7, but I know I can't always deploy against the latest version. And, more than that, I know I can work around those features. The code may look uglier, but it's usually as fast as it would be with the newest features.
And you are right - CPython is the canonical implementation of the language. The fact we can use a reference implementation in production environments is great.
You probably wouldn't be able to write something like Cassandra in Python 2.7 and expect it to run unmodified under Jython or IronPython, but you could write it in Python 2.5 and run it under both 2.7 CPython (with the expected multi-core annoyances) or under current Jython.
And you can't have painless C modules in Java either.
And you are right - CPython is the canonical implementation of the language. The fact we can use a reference implementation in production environments is great.
You probably wouldn't be able to write something like Cassandra in Python 2.7 and expect it to run unmodified under Jython or IronPython, but you could write it in Python 2.5 and run it under both 2.7 CPython (with the expected multi-core annoyances) or under current Jython.
And you can't have painless C modules in Java either.