code: def _credentials_modified_time(self) -> float:
      credentials_file = self._credentials_file()
      return os.stat(credentials_file).st_mtime
  
imports: import logging
  import os
  import threading
  import time
  from typing import Any
  import boto3
  from botocore import session
  from botocore.compat import ensure_unicode
  from botocore.credentials import CredentialProvider, Credentials, ReadOnlyCredentials, SharedCredentialProvider
  from botocore.session import get_session
label_desc: Use image node_id 4 for calling the RefreshableSharedCredentials obj's underlying member method code with example usage: obj._credentials_modified_time() and returns: os