The following results in a segfault on Linux with 2.3b1:
-------------------------
class StringDerived(str):
  __slots__ = ['a']
  def __init__(self, string):
    str.__init__(self, string)
    self.a = 1

class DerivedAgain(StringDerived):
  pass

o = DerivedAgain('hello world')
o.b = 2
--------------------------
Python 2.2.2 raises a TypeError when attempting to
derive a class from str with a non-empty __slots__,
maybe 2.3 should do the same?

I have no use case for deriving from str and defining
__slots__; I encountered the bug when writing test
cases for a debugger.