cdef class Foo(list): pass def foo(): f = Foo() f.append(1) gcc -g3 -fPIC -I/usr/include/python2.6 -g3 -W -Wall -c -o lll.o lll.c lll.c: In function ‘__pyx_pf_3lll_foo’: lll.c:468: error: ‘struct __pyx_obj_3lll_Foo’ has no member named ‘None’ Is this a known bug? -- vitja.