PYTHON setup.py build_ext --inplace

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

from Cython.Build import cythonize
from Cython.Distutils.extension import Extension

ext_modules = [
    Extension("a", ["a.pyx"]),
    Extension("x", ["x.pyx"]),
    Extension("y", ["y.pyx"]),
]

ext_modules = cythonize(ext_modules)

assert len(ext_modules[0].libraries) == 2
assert ext_modules[1].libraries == ["lib_x"]
assert ext_modules[2].libraries == ["lib_y"]

######## libx.pxd ########
# distutils: libraries = lib_x

######## liby.pxd ########
# distutils: libraries = lib_y

######## a.pyx ########
cimport libx , liby

######## x.pyx ########
cimport libx

######## y.pyx ########
cimport liby