code: def is_valid_user(self, user: str) -> bool:
      return user in self.user_dict
  
imports: import os, json, time
  import litellm
  from litellm.utils import ModelResponse
  import requests, threading
  from typing import Optional, Union, Literal
label_desc: Use image node_id 10 for calling the BudgetManager obj's underlying member method code with example usage: obj.is_valid_user(user) and returns: unknown