Question

I am trying to get the basic Cython tutorial to work. So I have

hello.pyx:

def say_hello_to(name):
    print("Hello %s!" % name)

And setup.py:

from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext

ext_modules = [Extension("hello", ["hello.pyx"])]

setup(
  name = 'Hello world app',
  cmdclass = {'build_ext': build_ext},
  ext_modules = ext_modules
)

However, trying to compile I get this error:

$ python setup.py build_ext --inplace
running build_ext
failed to import Cython: dlopen(/usr/local/lib/python2.7/site-packages/Cython/Compiler/Scanning.so, 2): Symbol not found: _PyCFunction_Check
  Referenced from: /usr/local/lib/python2.7/site-packages/Cython/Compiler/Scanning.so
  Expected in: flat namespace
 in /usr/local/lib/python2.7/site-packages/Cython/Compiler/Scanning.so
error: Cython does not appear to be installed

Cython is installed and scanning.so does appear to contain the symbol in question:

$ nm -gl /usr/local/lib/python2.7/site-packages/Cython/Compiler/Scanning.so | grep _PyCFunction_Check
             U _PyCFunction_Check

Any ideas? I’m on OS X 10.7.5 using homebrew python 2.7.3.

Edit: As pointed out by @bdash’ comment below, U _PyCFunction_Check actually means that _PyCFunction_Check is undefined.

Answer 1

The solution was very simple: I uninstalled the brew python and the pip-installed Cython and reinstalled both after which everything seem to work.

I think the problem was that I had installed python with brew having only Xcode installed. In the meantime – before I installed Cython – I installed Apple’s Command Line Tools. So python and Cython was installed under different conditions which probably led to the error.