There is a general way to cause unchecked infinite recursion at the C level, and I have no clue at the moment how it could be reasonably fixed.  The idea is to define special __xxx__ methods in such a way that no Python code is actually called before they invoke more special methods (e.g. themselves).

>>> class A: pass
>>> A.__mul__=new.instancemethod(operator.mul,None,A)
>>> A()*2
Segmentation fault