Unlike the canonical implementation, IronPython implements the str class as Unicode rather than an ASCII byte stream. While some are saying this is a serious fragmentation issue, others say it is no big deal.
The root of the issue is whether or not the str class must to be implemented as ASCII. While ASCII is severely limited in terms of supporting non-English languages, it can do so using code pages. ASCII strings can also be used to represent binary data as byte streams.
In non-canonical implementations like IronPython and JPython, the str class is implemented using the platform defined String class. In this case, that means Unicode strings. While this will not affect most applications, those that use str for non-English code pages or as byte arrays won't work.
Calvin Spealman argues this is a serious problem:
IronPython takes the syntax, but stops short of the language. The problem is one for both Python and IronPython lovers. In Python land, we're seeing what appears to be an influx of interest from the IronPython (also, via Silverlight) world, but all those new developers are creating completely incompatible code. IronPython advocates, on the other hand, look silly to think they are promoting the Python language, and are completely missing out on hundreds of great libraries, years of built up community, and synergy that isn't just a buzzword.
Response from the community have not been quite so negative. Michael Foord responds:
To make it clear - at Resolver we have a 'large' IronPython application, which uses many modules from the Python standard library as well as third party Python libraries - and it works *great*.
Manuel also defends the decision:
First of all, Python, CPython, IronPython, Jython, PyPy are all changing entities. As changing entities, we can only legitimately criticize their trajectories. I see zero evidence that IronPython will "fork" the Python community. So much activity is being spent to make the Python library run in IronPython, in the FePy community and in the Microsoft sanctioned community.
Even Guido van Rossum, the creator of Python himself, stepped in:
You realize that Jython has exactly the same str==unicode issue, right? I've endorsed this approach for both versions from the start. So I don't know what you are so bent out of shape about.
For the time being, it looks like the Python community is willing to accept some incompatibilities in exchange for support on more platforms.
