code: def expand_folder(files):
      
      expfiles = []
      for file in files:
          if os.path.isdir(file):
              for dirpath, dirnames, filenames in os.walk(file):
                  for filename in filenames:
                      expfiles.append(os.path.join(dirpath, filename))
          else:
              expfiles.append(file)
  
      for path in expfiles:
          if not os.path.exists(path):
              sys.stderr.write('%s: No such file or directory\n' % path)
  
      return expfiles
docs: Return a clone of file list files where all directories are recursively replaced with their contents.