challenging (?) metaclass problem

[alainpoint at yahoo.fr]

Hi,

I have what in my eyes seems a challenging problem.
Thanks to Peter Otten, i got the following code to work. It is a sort
of named tuple.
from operator import itemgetter
def constgetter(value):
	def get(self): return value
	return get
def createTuple(*names):
	class TupleType(type):
		pass
	class T(tuple):
		__metaclass__ = TupleType
		def __new__(cls, *args):
			if len(names) != len(args):
				raise TypeError
			return tuple.__new__(cls, args)
	for index, name in enumerate(names):
		setattr(T, name, property(itemgetter(index)))
		setattr(TupleType, name, property(constgetter(index)))
	return T
if __name__ == '__main__':
	Point=makeTuple('x','y')
	p=Point(4,7)
	assert p.x==p[0]
	assert p.y==p[1]
	assert Point.x==0
	assert Point.y==1

Now my problem is the following. I want to write a function called
createDerivedTuple in order to create a class derived from the one
created with the function createTuple, taking the parent class as first
argument:
def createDerivedTuple(parentclass,*names):
	....... code yet to be figured out ....

The usage should be as follows:

DerivedPoint=makeDerivedTuple(Point,'z')
p=DerivedPoint(4,7,9)
assert p.x==p[0]
assert p.y==p[1]
assert p.z==p[2]
assert DerivedPoint.x==0
assert DerivedPoint.y==1
assert DerivedPoint.z==2

I am still a newbie on metaclasses but i am convinced there are elegant
solutions to this challenging problem.

Best regards

Alain