code: def on_tool_start(
      self, serialized: Dict[str, Any], input_str: str, **kwargs: Any
  ) -> None:
      self._require_current_thought().on_tool_start(
          serialized, input_str, **kwargs
      )
  
imports: from __future__ import annotations
  import time
  from enum import Enum
  from typing import TYPE_CHECKING, Any, Dict, List, NamedTuple, Optional
  from langchain.callbacks.base import BaseCallbackHandler
  from langchain.schema import AgentAction, AgentFinish, LLMResult
  from streamlit.runtime.metrics_util import gather_metrics
label_desc: Use image node_id 9 for calling the StreamlitCallbackHandler obj's underlying member method code with example usage: obj.on_tool_start(serialized, input_str) without return types