Python distutils example for adding flags per the compiler that is **going** to be used (not the default).

setup_custom_compiler_flags.py

from setuptools import setup, Extension
from setuptools.command.build_ext import build_ext

copt = {
    'msvc': ['/openmp', '/Ox', '/fp:fast','/favor:INTEL64','/Og'],
    'mingw32' : ['-fopenmp','-O3','-ffast-math','-march=native']
}
lopt = {
    'mingw32' : ['-fopenmp']
}

class build_ext_subclass(build_ext):
    def build_extensions(self):
        c = self.compiler.compiler_type
        if copt.has_key(c):
           for e in self.extensions:
               e.extra_compile_args += copt[c]
        if lopt.has_key(c):
            for e in self.extensions:
                e.extra_link_args += lopt[c]
        build_ext.build_extensions(self)

mod = Extension(
    '_wripaca',
    sources=[
        '../wripaca_wrap.c', 
        '../../src/wripaca.c'
    ],
    include_dirs=['../../include']
)

setup(
    name = 'wripaca',
    ext_modules = [mod],
    py_modules = ["wripaca"],
    cmdclass = {'build_ext': build_ext_subclass}
)

setup_custom_compiler_flags_v2.py

from setuptools import setup, Extension
from setuptools.command.build_ext import build_ext

from distutils.ccompiler import CCompiler
from distutils.unixccompiler import UnixCCompiler
from distutils.msvccompiler import MSVCCompiler

DEBUG = False

compiler_opts = {
    CCompiler: {},
    MSVCCompiler: {
        'extra_compile_args': ['/EHsc'],
    },
}

if DEBUG:
    compiler_opts = {
        CCompiler: {'define_macros': [('DEBUG_chardet', '1')]},
        MSVCCompiler: {
            'extra_compile_args': ['/EHsc', '/Z7'],
            'extra_link_args': ['/DEBUG'],
        },
        UnixCCompiler: {
            'extra_compile_args': ['-g'],
            'extra_link_args': ['-g'],
        }
    }

class build_ext_subclass(build_ext):
    def build_extensions(self):
        c = self.compiler

        opts = [v for k, v in compiler_opts.items() if isinstance(c, k)]
        for e in self.extensions:
            for o in opts:
                for attrib, value in o.items():
                    getattr(e, attrib).extend(value)

        build_ext.build_extensions(self)

mod = Extension(
    '_wripaca',
    sources=[
        '../wripaca_wrap.c', 
        '../../src/wripaca.c'
    ],
    include_dirs=['../../include']
)

setup(
    name = 'wripaca',
    ext_modules = [mod],
    py_modules = ["wripaca"],
    cmdclass = {'build_ext': build_ext_subclass}
)