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: Try setting the "CC" and "CXX" environment variables from inside the setup.py
with os.environ.

