clang error when installing pygresql under Mac OS

I was trying to install PyGreSQL under Mac OS X(10.11.3), but the same clang error occurs when installing from pip and source.

$ python3 setup.py install
running install
running bdist_egg
running egg_info
writing PyGreSQL.egg-info/PKG-INFO
writing top-level names to PyGreSQL.egg-info/top_level.txt
writing dependency_links to PyGreSQL.egg-info/dependency_links.txt
reading manifest file 'PyGreSQL.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
writing manifest file 'PyGreSQL.egg-info/SOURCES.txt'
installing library code to build/bdist.macosx-10.6-intel/egg
running install_lib
running build_py
running build_ext
building '_pg' extension
/usr/bin/clang -fno-strict-aliasing -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -g -DPYGRESQL_VERSION=5.0 -DDIRECT_ACCESS -DLARGE_OBJECTS -DDEFAULT_VARS -DESCAPING_FUNCS -I/Library/Frameworks/Python.framework/Versions/3.5/include/python3.5m -I/Library/PostgreSQL/9.5/include -I/Library/Frameworks/Python.framework/Versions/3.5/include/python3.5m -c pgmodule.c -o build/temp.macosx-10.6-intel-3.5/pgmodule.o -O2 -funsigned-char -Wall -Werror
pgmodule.c:3684:3: error: code will never be executed [-Werror,-Wunreachable-code]
                long    num_rows;
                ^~~~~~~~~~~~~~~~~
1 error generated.
error: command '/usr/bin/clang' failed with exit status 1

clang error occurs when installing PyGreSQL

I already had PyGreSQL, Xcode and Xcode tools installed in my machine, and I also added the bin directory of PostgreSQL to $PATH.

I was able to compile the module by editing the modules's setup.py

Find the line

extra_compile_args = ....

It's a list of extra compile arguments to pass to clang. One of the extra arguments will be -Werror, which means "treat all warnings as ERRORS". And as you know an error will abort compilation.

Remove that line, and run python3 setup.py build again and you'll see the same line appears, but this time as a warning, and everything goes okay!