How to tell distutils to use gcc?

Question

I want to wrap a test project containing C++ and OpenMP code with Cython, and build it with distutils via a setup.py file. The content of my file looks like this:

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


modules = [Extension("Interface",
                     ["Interface.pyx", "Parallel.cpp"],
                     language = "c++",
                     extra_compile_args=["-fopenmp"],
                     extra_link_args=["-fopenmp"])]

for e in modules:
    e.cython_directives = {"embedsignature" : True}

setup(name="Interface",
     cmdclass={"build_ext": build_ext},
     ext_modules=modules)

The -fopenmp flag is used with gcc to compile and link against OpenMP. However, if I just invoke

cls ~/workspace/CythonOpenMP/src $ python3 setup.py build

this flag is not recognized, because the compiler is clang:

running build
running build_ext
skipping 'Interface.cpp' Cython extension (up-to-date)
building 'Interface' extension
cc -Wno-unused-result -fno-common -dynamic -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -I/usr/local/include -I/usr/local/opt/sqlite/include -I/usr/local/Cellar/python3/3.3.0/Frameworks/Python.framework/Versions/3.3/include/python3.3m -c Interface.cpp -o build/temp.macosx-10.8-x86_64-3.3/Interface.o -fopenmp
clang: warning: argument unused during compilation: '-fopenmp'
cc -Wno-unused-result -fno-common -dynamic -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -I/usr/local/include -I/usr/local/opt/sqlite/include -I/usr/local/Cellar/python3/3.3.0/Frameworks/Python.framework/Versions/3.3/include/python3.3m -c Parallel.cpp -o build/temp.macosx-10.8-x86_64-3.3/Parallel.o -fopenmp
clang: warning: argument unused during compilation: '-fopenmp'
Parallel.cpp:24:10: warning: unknown pragma ignored [-Wunknown-pragmas]
        #pragma omp parallel for
                ^
1 warning generated.
c++ -bundle -undefined dynamic_lookup -L/usr/local/lib -L/usr/local/opt/sqlite/lib build/temp.macosx-10.8-x86_64-3.3/Interface.o build/temp.macosx-10.8-x86_64-3.3/Parallel.o -o build/lib.macosx-10.8-x86_64-3.3/Interface.so -fopenmp
ld: library not found for -lgomp
clang: error: linker command failed with exit code 1 (use -v to see invocation)
error: command 'c++' failed with exit status 1

I've unsucessfully tried to specify gcc:

cls ~/workspace/CythonOpenMP/src $ python3 setup.py build --compiler=g++-4.7
running build
running build_ext
error: don't know how to compile C/C++ code on platform 'posix' with 'g++-4.7' compiler

How can I tell distutils to use gcc?

Answer 1

Try setting the "CC" environment variable from inside the setup.py with os.environ.