PYTHON setup.py build_ext --inplace
PYTHON test.py

######## setup.py ########
from Cython.Build import cythonize
from distutils.core import setup

setup(
  ext_modules = cythonize("*.pyx"),
)

######## test.py ########
from base import A, B
from derived import C

assert B().foo() == 'B.foo'
assert C().foo() == 'B.foo'

assert A().foo1() == 'A.foo'
assert B().foo1() == 'B.foo'
assert C().foo1() == 'B.foo'

assert B().foo2() == 'B.foo'
assert C().foo2() == 'B.foo'

assert C().bar() == 'C.bar'

######## base.pxd ########
cdef class A(object):
    cdef foo(self)

cdef class B(A):
    cpdef foo(self)

######## base.pyx ########
cdef class A(object):
    cdef foo(self):
        return "A.foo"

    def foo1(self):
        return self.foo()

cdef class B(A):
    cpdef foo(self):
        return "B.foo"

    def foo2(self):
        return self.foo()

######## derived.pyx ########
from base cimport B

cdef class C(B):
    cpdef bar(self):
        return "C.bar"