[whateverer]

But isn't Jython years behind the CPython version, PyPy still experimental and on Python 2.x, and IronPython mostly a novelty? Stackless seems in better shape, though, and couldn't say anything in respect to usage.

The argument for Java is clearer and it's a well known case of the interaction of multiple implementors, and thus it has an standardization process.

[mbell]

I would say that CPython, PyPy and Stackless are in pretty strong competition in different areas. PyPy only supporting 2.x seems to be a relatively unimportant metric given the slow adoption of 3.x. As for it being experimental, perhaps technically but I do believe its used in production in many places. From what I know Stackless gets a large portion of its support from CCP games due to its use in Eve Online. I'm sure there are others but its use case is relatively unique.

[stcredzero]

In the grand scheme of things, the differences between CPython and PyPy are minor. Stackless is a special case. Relatively Python has very little language fragmentation. It has more of what I'd call "implementation fragmentation," but not too much of that either.

[vgnet]

FWIW, PyPy is close to supporting 3.x (for x ~ 2 IIRC): http://morepypy.blogspot.com/2012/04/py3k-status-update-3.ht...