New to Cython...can't seem to properly wrap enums

Question

I'm pretty new to Cython but I'm trying to learn more, as I'd like to be able to call a fairly large and complicated set of C/C++ code directly from Python.

I've been able to run through the examples OK and have even been able to wrap a very small part of the main project on which I'm working. But I've gotten stuck on wrapping enums.

I've tried to break out what I'm trying in a very simplified example.

Here is the C code, in myenum.h

// myenum.h
enum strategy {
    slow = 0,
    medium = 1,
    fast = 2
};

Here is what I thought would work as a wapper in pymyenum.pyx

# distutils: language = c
cdef extern from "myenum.h" namespace "myenum":
    cdef enum strategy:
        slow,
        medium,
        fast

And here is my setup.py

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

setup(ext_modules = cythonize(
    "pymyenum.pyx",                 # our Cython source
    sources=["myenum.h"],  # additional source file(s)
    language="c",             # generate C code
    ))

In this directory, I run

python setup.py build_ext --inplace

and I get my pymyenum.so, that I can import! Yeah! But I can't access strategy.

In [1]: import pymyenum

In [2]: pymyenum.
pymyenum.c    pymyenum.pyx  pymyenum.so

In [2]: pymyenum.strategy
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-80980071607b> in <module>()
----> 1 pymyenum.strategy

AttributeError: 'module' object has no attribute 'strategy'

In [3]: from pymyenum import strategy
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-3-9bae6637f005> in <module>()
----> 1 from pymyenum import strategy

ImportError: cannot import name strategy

I can't seem to find the right example to get me out of this. Thanks in advance for anyone who can help!

Matt

Answer 1

It will work how you want if you use this pymyenum.pyx:

# distutils: language = c
cdef extern from "myenum.h":
    cpdef enum strategy:
        slow,
        medium,
        fast

Note that your header is a c header with no 'myenum' namespace, and it's cpdef for anything you want exported to python. cdef just makes things available in cython code.