Why does Cython compiler generate like this with 'cpython-35m-x86_64-linux-gnu.so' suffix

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

setup(
    cmdclass = {'build_ext': build_ext}, 
    ext_modules = [Extension("module_name", ["xxxx.pyx", './yyyyy.c'],
                    language='c',
                    extra_compile_args = ['-std=gnu11'],
                    extra_link_args=['-std=gnu11']                 
                    )]
)


$ python --version
Python 3.5.1
$ python -c "import cython; print(cython.__version__);"
0.25.2
$ python setup.py build_ext -i

      

        
        
        
      

    

Questions> Why does Cython generate module name like module_name.cpython-35m-x86_64-linux-gnu.so

instead module_name.so

?

thank