code: def addpackage(sys_sitedir, pthfile, known_dirs):
      
      with open(join(sys_sitedir, pthfile)) as f:
          for n, line in enumerate(f):
              if line.startswith("#"):
                  continue
              line = line.rstrip()
              if line:
                  if line.startswith(("import ", "import\t")):
                      exec (line, globals(), locals())
                      continue
                  else:
                      p_rel = join(sys_sitedir, line)
                      p_abs = abspath(line)
                      if isdir(p_rel):
                          os.environ['PATH'] += env_t(os.pathsep + p_rel)
                          sys.path.append(p_rel)
                          added_dirs.add(p_rel)
                      elif isdir(p_abs):
                          os.environ['PATH'] += env_t(os.pathsep + p_abs)
                          sys.path.append(p_abs)
                          added_dirs.add(p_abs)
  
      if isfile(pthfile):
          site.addpackage(sys_sitedir, pthfile, known_dirs)
      else:
          logging.debug("pth file '%s' not found")
docs: Wrapper for site.addpackage
  
      Try and work out which directories are added by
      the .pth and add them to the known_dirs set
  
      :param sys_sitedir: system site-packages directory
      :param pthfile: path file to add
      :param known_dirs: set of known directories