code: def _format_add_colon_space_single(
      system_message: str,
      messages: List[Tuple[str, Optional[str]]],
      sep: str,
  ) -> str:
      """Format the prompt with the add-colon-space-single style."""
      ret = system_message + sep
      for role, message in messages:
          if message:
              ret += role + ": " + message + sep
          else:
              ret += role + ": "  # must be end with a space
      return ret
  
imports: from __future__ import annotations
  import os
  import json
  import ctypes
  import dataclasses
  from typing import Any, Dict, Iterator, List, Optional, Tuple, Union, Protocol
  import llama_cpp.llama
  import llama_cpp.llama_types
  import llama_cpp.llama_grammar
  from ._utils import suppress_stdout_stderr
label_desc: Use image node_id 9 for calling a global function with example usage: _format_add_colon_space_single(system_message, messages, sep) and returns: ret