Porting to Py3K, I modified a function like the followin, using a trick for it working in Py2.x . def __iter__(self): if self == _mpi.INFO_NULL: return try: range = xrange except: pass nkeys = _mpi.info_get_nkeys(self) for nthkey in range(nkeys): yield _mpi.info_get_nthkey(self, nthkey) However, I've got in my unittests (running with py3k) ERROR: testPyMethods (__main__.TestInfo) ---------------------------------------------------------------------- Traceback (most recent call last): File "tests/unittest/test_info.py", line 123, in testPyMethods for key in INFO: File "/u/dalcinl/lib/python/mpi4py/MPI.py", line 937, in __iter__ for nthkey in range(nkeys): UnboundLocalError: local variable 'range' referenced before assignment I am not completelly sure if this is expected (it is, regarding implementation, but perhaps not regarding Python as a language), so I post this for your consideration. -- Lisandro Dalcín --------------- Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC - Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54-(0)342-451.1594