nodes: 0, module; 1, function_definition; 2, function_name:get_atom_type_symbol; 3, parameters; 4, block; 5, identifier:cls; 6, identifier:calc; 7, dictionary_splat_pattern; 8, expression_statement; 9, expression_statement; 10, expression_statement; 11, if_statement; 12, return_statement; 13, identifier:kwargs; 14, comment:"""
          Returns a list of atom types. Each atom site MUST occur only
          once in this list. List MUST be sorted.
          """; 15, assignment; 16, assignment; 17, comparison_operator:'basis_set' not in dictionary.keys(); 18, block; 19, call; 20, identifier:parameters; 21, attribute; 22, identifier:dictionary; 23, call; 24, string; 25, call; 26, return_statement; 27, identifier:sorted; 28, argument_list; 29, attribute; 30, identifier:output; 31, attribute; 32, argument_list; 33, string_content:basis_set; 34, attribute; 35, argument_list; 36, None; 37, call; 38, identifier:calc; 39, identifier:out; 40, identifier:parameters; 41, identifier:get_dict; 42, identifier:dictionary; 43, identifier:keys; 44, attribute; 45, argument_list; 46, subscript; 47, identifier:keys; 48, identifier:dictionary; 49, string; 50, string_content:basis_set
code: def get_atom_type_symbol(cls,calc,**kwargs):
          """
          Returns a list of atom types. Each atom site MUST occur only
          once in this list. List MUST be sorted.
          """
          parameters = calc.out.output
          dictionary = parameters.get_dict()
          if 'basis_set' not in dictionary.keys():
              return None
          return sorted(dictionary['basis_set'].keys())