nodes: 0, module; 1, function_definition; 2, function_name:get_signed_headers; 3, parameters; 4, block; 5, identifier:headers; 6, expression_statement; 7, expression_statement; 8, for_statement; 9, return_statement; 10, comment:"""
      Get signed headers.
  
      :param headers: input dictionary to be sorted.
      """; 11, assignment; 12, identifier:header; 13, identifier:headers; 14, block; 15, call; 16, identifier:signed_headers; 17, list; 18, expression_statement; 19, identifier:sorted; 20, argument_list; 21, call; 22, identifier:signed_headers; 23, attribute; 24, argument_list; 25, identifier:signed_headers; 26, identifier:append; 27, call; 28, attribute; 29, argument_list; 30, call; 31, identifier:strip; 32, attribute; 33, argument_list; 34, identifier:header; 35, identifier:lower
code: def get_signed_headers(headers):
      """
      Get signed headers.
  
      :param headers: input dictionary to be sorted.
      """
      signed_headers = []
      for header in headers:
          signed_headers.append(header.lower().strip())
      return sorted(signed_headers)