PYTHON setup.py build_ext --inplace
PYTHON -c "import a"

######## setup.py ########

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

# Add ./site-packages to sys.path
from os.path import realpath
import sys
sys.path.append(realpath('site-packages'))

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

######## site-packages/b/__init__.py ########

######## site-packages/b/other.pxd ########

cdef extern from "foo.c":
    int foo(int)

######## site-packages/b/foo.c ########

static int foo(int a)
{
    return a * a;
}

######## a.pyx ########

from b.other cimport foo
print foo(10)

cimport b.other
print b.other.foo(10)