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: Return the state or widget value with the given key.
  
  Raises
  ------
  StreamlitAPIException
      If the key is not a valid SessionState user key.
docstr_tok: ["Return","the","state","or","widget","value","with","the","given","key",".","Raises","--","--","--","StreamlitAPIException","If","the","key","is","not","a","valid","SessionState","user","key","."]
code: def __getitem__(self, key: Key) -> Any:
      """Return the state or widget value with the given key.
  
      Raises
      ------
      StreamlitAPIException
          If the key is not a valid SessionState user key.
      """
      key = str(key)
      require_valid_user_key(key)
      return get_session_state()[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 4 for calling the SessionStateProxy obj's underlying member method code with example usage: obj.__getitem__(key) and returns: get_session_state