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).
docstr: Number of user state and keyed widget values in session_state.
docstr_tok: ["Number","of","user","state","and","keyed","widget","values","in","session_state","."]
code: def __len__(self) -> int:
      """Number of user state and keyed widget values in session_state."""
      return len(get_session_state().filtered_state)
  
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 2 for calling the SessionStateProxy obj's underlying member method code with example usage: obj.__len__() and returns: len