Hi, I have been scratching my head on the following problem. I am designing a new array iterator, in C, to walk into a neighborhood of an array. I would like this iterator to 'inherit' from PyArrayIterObject, so that I can design some API which accept both PyArrayIterObject and PyArrayNeighIterObject (through pointer casting). I have tried something like: typedef struct { /* first item is the base class, so that casting a PyArrayNeighIterObject* to PyArrayIterObject* works */ PyArrayIterObject base; /* PyArrayNeighIterObject specific members */ .... } PyArrayNeighIterObject; But this forces me to cast a PyArrayNeighIterObject* to PyArrayIterObject whenever I want to access members of the base instance. The alternative is to copy the PyArrayIterObject members by hand, as is currently done in numpy itself (for broadcasting iterator PyArrayMapIterObject). But since my iterator lives outside numpy, this is really error-prone IMHO - there will be crashes whenever the PyArrayIterObject struct changes in an ABI incompatible way, and this may be quite hard to debug Is there a better way ? David