Last August, James Knight posted to python-dev, "There's a fair number of classes that claim they are defined in __builtin__, but do not actually appear there". There was a discussion and James submitted this patch:
The final result of the discussion is unclear. Guido declared himself +0.5 on the concept, but nobody has reviewed the patch in detail yet.
The original email thread starts here:
The patch still applies, and test cases still run OK afterwards.
Now that 2.4 has been released it is perhaps a good time to discuss in on python-dev again. If it isn't discussed, then the patch should be closed due to lack of interest.