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When trying to create a sub-subclass of a ctypes.Structure, the behavior
is not as expected.
An executable example that describes the problem in detail and
demonstrates the issue is available at
http://paste.turbogears.org/paste/29555 and also attached.
The failing behavior is near the beginning, following the description.
Three unsuccessful workarounds follow.
The expected behavior is found at the end, where a final workaround has
been implemented.
Can this behavior be improved in subsequent releases of ctypes? If not,
can ctypes at least support the workaround natively (perhaps by
providing a method in the Structure class that performs the workaround
and can be called by a sub-subclass during __init__)?

The problem is the implementation of the current __init__ method, in
Modules/_ctypes/_ctypes.c, line 4024. Rewritten in Python, and slightly
simplified it looks like this:
 def __init__(self, *args, **kw):
 """The current BUGGY __init__ method"""
 names = [f[0] for f in self._fields_]
 for n, v in zip(names, args):
 setattr(self, n, v)
 for n, v in kw.iteritems():
 setattr(self, n, v)
It assigns positional parameters to the names found in the _fields_ list
of the subclass, but it should look up all the _fields_ definitions in
all the superclasses, too. Working pseudo Python code:
 def __init__(self, *args, **kw):
 """This is how the Structure's __init__method SHOULD be"""
 if args:
 names = []
 for tp in self.__class__.mro()[2::-1]:
 for n, _ in tp._fields_:
 names.append(n)
 for n, v in zip(names, args):
 setattr(self, n, v)
 for n, v in kw.iteritems():
 setattr(self, n, v)
Now, I don't really want to write the above code in C ;-).

Heh. Me neither.
Is it possible to use something like Cython to generate the C code?

That was easier than I thought. The generated code is _ugly_ but it did
seem to be able to generate it.
I created init.pyx
{{{
class X(object):
	def __init__(self, *args, **kw):
		"""This is how the Structure's __init__method SHOULD be"""
		if args:
			names = []
			for tp in self.__class__.mro()[2::-1]:
				for n, _ in tp._fields_:
					names.append(n)
			for n, v in zip(names, args):
				setattr(self, n, v)
		for n, v in kw.iteritems():
			setattr(self, n, v)
}}}
Then, ran cython init.pyx and got the attached file.
Is that any help?

> Is that any help?
Not really ;-).
Here is a patch I just wrote - it must still be checked for correctness,
and tests for it must be added. I hope the comment in the code explains
how it works. ctypes-structinit.patch

I've commited a slightly changed patch plus a test.
trunk: 74917, py3k: 74918, release26-maint: 74919, release31-maint: 74920.