python_c_extension | extends python with C : c-api , ctypes and Cython | REST library

The error message says:

version.replace(' ','.') AttributeError: 'float' object has no attribute 'replace'

Your build script says:

The essential problem here is that when setup.py links your extension it's putting -lcrypto on the command line before the object file with your code in it. The Unix linker processes objects and libraries strictly left to right on the command line: -lcrypto foo.o will not use libcrypto to resolve symbols in foo.o. This is for historical reasons and no longer makes a whole lot of sense but we're stuck with it because it would break too many Makefiles to change it. Also for historical reasons which no longer make a whole lot of sense, if you don't put -Wl,-z,defs on the command line, a shared library (compiled-code Python extensions are technically shared libraries) with undefined symbols in it isn't a link-time error, which is why the build appeared to work.

Your extension intrinsically requires libcrypto. If I am reading the Distutils documentation correctly, that means you should specify it in the libraries= keyword argument to Extension(...) rather than putting it in CFLAGS. Like this: