The fix for bug http://python.org/sf/451547 has made
the follow sequence fail:

>>> import pickle, copy
>>> o = copy._EmptyClass()
>>> reload(copy)
<module 'copy' from '/usr/lib/python2.2/copy.pyc'>
>>> pickle.dumps(o, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.2/pickle.py", line 978, in dumps
    Pickler(file, bin).dump(object)
  File "/usr/lib/python2.2/pickle.py", line 115, in dump
    self.save(object)
  File "/usr/lib/python2.2/pickle.py", line 225, in save
    f(self, object)
  File "/usr/lib/python2.2/pickle.py", line 477, in
save_inst
    save(cls)
  File "/usr/lib/python2.2/pickle.py", line 225, in save
    f(self, object)
  File "/usr/lib/python2.2/pickle.py", line 524, in
save_global
    raise PicklingError(
pickle.PicklingError: Can't pickle <class
copy._EmptyClass at 0x819478c>: it's not the same
object as copy._EmptyClass

Looking at bug 451547 the reported problem was that
pickle would allow you to dump lambdas.  When you try
to dump lambdas you now see the following:

>>> f = lambda x: x in (1,2,3)
>>> s = pickle.dumps(f, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.2/pickle.py", line 978, in dumps
    Pickler(file, bin).dump(object)
  File "/usr/lib/python2.2/pickle.py", line 115, in dump
    self.save(object)
  File "/usr/lib/python2.2/pickle.py", line 225, in save
    f(self, object)
  File "/usr/lib/python2.2/pickle.py", line 519, in
save_global
    raise PicklingError(
pickle.PicklingError: Can't pickle <function <lambda>
at 0x8157edc>: it's not found as __main__.<lambda>

The reported lambda problem is found without having to
check that the manually resolved class object is at the
same memory address as the class object referenced by
the lambda.  I think the pickle code is being too careful.

From pickle.py: the "klass is not object" test in the
else clause should probably be removed.

        try:
            __import__(module)
            mod = sys.modules[module]
            klass = getattr(mod, name)
        except (ImportError, KeyError, AttributeError):
            raise PicklingError(
                "Can't pickle %r: it's not found as
%s.%s" %
                (object, module, name))
        else:
            if klass is not object:
                raise PicklingError(
                    "Can't pickle %r: it's not the same
object as %s.%s" %
                    (object, module, name))

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It's still there for 2.3b1.  It seems to pickle without raising an error when it 
uses the text format.

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Won't fix. If still annoyed with this behaviour, please
follow the GvR's directives at bug #451547.