class_docstr: A stateless singleton that proxies `st.session_state` interactions
  to the current script thread's SessionState instance.
  
  The proxy API differs slightly from SessionState: it does not allow
  callers to get, set, or iterate over "keyless" widgets (that is, widgets
  that were created without a user_key, and have autogenerated keys).
code: def __getattr__(self, key: str) -> Any:
      try:
          return self[key]
      except KeyError:
          raise AttributeError(_missing_attr_error_message(key))
  
imports: from typing import Any, Dict, Iterator, MutableMapping
  from typing_extensions import Final
  from streamlit import logger
  from streamlit import runtime
  from streamlit.runtime.metrics_util import gather_metrics
  from streamlit.runtime.state.common import require_valid_user_key
  from streamlit.runtime.state.safe_session_state import SafeSessionState
  from streamlit.runtime.state.session_state import SessionState
  from streamlit.type_util import Key
label_desc: Use image node_id 7 for calling the SessionStateProxy obj's underlying member method code with example usage: obj.__getattr__(key) and returns: self