Aahz said:

Any reason we can't require importer objects to be new-style classes, which could then use __new__? (I vaguely recall some discussion about this, but it should be documented in the PEP.)

Basically, why bother? It just makes writing importers (mildly) more complex (most people know about __init__ whereas __new__ is ... err ... newer), where the existing proposal works fine. But you're right, a comment in the PEP would be good. Paul