[Python-Dev] Pickling objects that return string from reduce

[Bruce Christensen]

I'm still plugging away on IronPython's cPickle, and I've stumbled
across another ambiguity in the pickle docs. From
http://docs.python.org/lib/node69.html:

"If a string is returned, it names a global variable whose contents are
pickled as normal. The string returned by __reduce__ should be the
object's local name relative to its module; the pickle module searches
the module namespace to determine the object's module."

What exactly does that last clause mean? Must the object have a
__module__ attribute? What if it doesn't? What if the module exists but
isn't currently imported? 

Is something like the following close?

    # Call copy_reg-registered func, obj.__reduce_ex__, or
obj.__reduce__
    result = call_reduce(obj)

    if type(result) == tuple:
        ... (do appropriate things here)
    elif isinstance(result, basestring):
        name = result
        module = "<unknown module>"
        try:
            module = obj.__module__
            found_obj = getattr(sys.modules[module], name)
        except AttributeError, KeyError:
            raise PicklingError(
                "Can't pickle %r: it's not found as %s.%s"
                % (obj, module, name)
                )

        if found_obj is not obj:
            raise PicklingError(
                "Can't pickle %r: it's not the same object as %s.%s"
                % (obj, module, name)
                )

        emit("c%s\n%s\n" % module, name)

Thanks,

--Bruce