static - How to statically link a library when compiling a python module extension

Question

I would like to modify a setup.py file such that the command "python setup.py build" compiles a C-based extension module that is statically (rather than dynamically) linked to a library.

The extension is currently dynamically linked to a number of libraries. I would like to leave everything unchanged except for statically linking to just one library. I have successfully done this by manually modifying the call to gcc that distutils runs, although it required that I explicitly listed the dependent libraries.

Perhaps this is too much information, but for clarity this is the final linking command that was executed during the "python setup.py build" script:

gcc -pthread -shared -L/system/lib64 -L/system/lib/ -I/system/include build/temp.linux-x86_64-2.7/src/*.o -L/system/lib -L/usr/local/lib -L/usr/lib -ligraph -o build/lib.linux-x86_64-2.7/igraph/core.so

And this is my manual modification:

gcc -pthread -shared -L/system/lib64 -L/system/lib/ -I/system/include build/temp.linux-x86_64-2.7/src/*.o -L/system/lib -L/usr/local/lib -L/usr/lib /system/lib/libigraph.a -lxml2 -lz -lgmp -lstdc++ -lm -ldl -o build/lib.linux-x86_64-2.7/igraph/core.so

Section 2.3.4 of Distributing Python Modules discusses the specification of libraries, but only "library_dirs" is appropriate and those libraries are dynamically linked.

I'm using a Linux environment for development but the package will also be compiled and installed on Windows, so a portable solution is what I'm after.

Can someone tell me where to look for instructions, or how to modify the setup.py script? (Thanks in advance!)

I'm new to StackOverflow, so my apologies if I haven't correctly tagged this question, or if I have made some other error in this posting.

Answer 1

6 - 7 years later, static linking with Python extensions is still poorly documented. As the OP points out in a comment, the usage is OS dependend.

On Linux / Unix

Static libraries are linked just as object files and should go with the path and its extension into extra_objects.

On Windows

The compiler sees if the linked library is static or dynamic and the static library name goes to the libraries list and the directories to library_dir

Solution for both platforms

For the example below, I will use the same library scenario as OP, linking igraph static and z, xml2 and gmp dynamic. This solution is a bit hackish, but at least does for each platform the right thing.

static_libraries = ['igraph']
static_lib_dir = '/system/lib'
libraries = ['z', 'xml2', 'gmp']
library_dirs = ['/system/lib', '/system/lib64']

if sys.platform == 'win32':
    libraries.extend(static_libraries)
    library_dirs.append(static_lib_dir)
    extra_objects = []
else: # POSIX
    extra_objects = ['{}/lib{}.a'.format(static_lib_dir, l) for l in static_libraries]

ext = Extension('igraph.core',
                 sources=source_file_list,
                 libraries=libraries,
                 library_dirs=library_dirs,
                 include_dirs=include_dirs,
                 extra_objects=extra_objects)

On MacOS

I guess this works also for MacOS (using the else path) but I have not tested it.