code: def use_built_igraph(self):
          
          buildcfg.include_dirs = [os.path.join("igraphcore", "include")]
          buildcfg.library_dirs = [os.path.join("igraphcore", "lib")]
          buildcfg.static_extension = True
  
          buildcfg_file = os.path.join("igraphcore", "build.cfg")
          if os.path.exists(buildcfg_file):
              buildcfg.libraries = eval(open(buildcfg_file).read())
docs: Assumes that igraph is built already in ``igraphcore`` and sets up
          the include and library paths and the library names accordingly.