code: def get_importable_files(folder):
      
      for fname in os.listdir(folder):
          if fname.endswith('.py') and not fname.startswith('_'):
              fullname = os.path.join(folder, fname)
              if check_writable_by_others(fullname):
                  print("ERROR: refuse to load module from world writable file %r" % fullname)
              else:
                  yield fname
docs: Find all module files in the given folder that end with '.py' and
      don't start with an underscore.
      @return module names
      @rtype: iterator of string