[issue3122] sys.getsizeof() gives an AttributeError for _sre objects.

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc <amauryfa at gmail.com> added the comment:

I wondered why getsizeof fails for _sre.SRE_Pattern objects when it
succeeds for _socket.socket or struct.Struct.

It turns out that _sre.SRE_Pattern defines the tp_getattr slot, and this
prevents attribute lookup from searching the base class (object).
This is a pity, because the base implementation (which use tp_basicsize)
does the right thing for many objects.

So I borrowed some code from the __format__ method, and here is a patch.
Now classes are not handled specially any more; the distinction is
between old-style instances, and all other objects.

All tests pass, but I may have missed something important...

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nosy: +amaury.forgeotdarc
Added file: http://bugs.python.org/file10746/sizeof.patch

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