docstr: True if the singleton Runtime instance has been created.
  
  When a Streamlit app is running in "raw mode" - that is, when the
  app is run via `python app.py` instead of `streamlit run app.py` -
  the Runtime will not exist, and various Streamlit functions need
  to adapt.
code: def exists(cls) -> bool:
      """True if the singleton Runtime instance has been created.
  
      When a Streamlit app is running in "raw mode" - that is, when the
      app is run via `python app.py` instead of `streamlit run app.py` -
      the Runtime will not exist, and various Streamlit functions need
      to adapt.
      """
      return cls._instance is not None
  
imports: from __future__ import annotations
  import asyncio
  import time
  import traceback
  from dataclasses import dataclass, field
  from enum import Enum
  from typing import TYPE_CHECKING, Awaitable, Dict, NamedTuple, Optional, Tuple, Type
  from typing_extensions import Final
  from streamlit import config
  from streamlit.logger import get_logger
  from streamlit.proto.BackMsg_pb2 import BackMsg
  from streamlit.proto.ForwardMsg_pb2 import ForwardMsg
  from streamlit.runtime.app_session import AppSession
  from streamlit.runtime.caching import get_data_cache_stats_provider, get_resource_cache_stats_provider
  from streamlit.runtime.caching.storage.local_disk_cache_storage import LocalDiskCacheStorageManager
  from streamlit.runtime.forward_msg_cache import ForwardMsgCache, create_reference_msg, populate_hash_if_needed
  from streamlit.runtime.legacy_caching.caching import _mem_caches
  from streamlit.runtime.media_file_manager import MediaFileManager
  from streamlit.runtime.media_file_storage import MediaFileStorage
  from streamlit.runtime.memory_session_storage import MemorySessionStorage
  from streamlit.runtime.runtime_util import is_cacheable_msg
  from streamlit.runtime.script_data import ScriptData
  from streamlit.runtime.scriptrunner.script_cache import ScriptCache
  from streamlit.runtime.session_manager import ActiveSessionInfo, SessionClient, SessionClientDisconnectedError, SessionManager, SessionStorage
  from streamlit.runtime.state import SCRIPT_RUN_WITHOUT_ERRORS_KEY, SessionStateStatProvider
  from streamlit.runtime.stats import StatsManager
  from streamlit.runtime.uploaded_file_manager import UploadedFileManager
  from streamlit.runtime.websocket_session_manager import WebsocketSessionManager
  from streamlit.watcher import LocalSourcesWatcher
label_desc: Use image node_id 2 for calling the Runtime obj's underlying member method code with example usage: obj.exists(cls) and returns: unknown