docstr: Initialize state data once.
docstr_tok: ["Initialize","state","data","once","."]
code: def __call__(self, **kwargs):
      """Initialize state data once."""
      for item, value in kwargs.items():
          if item not in self._state["data"]:
              self._state["data"][item] = value
  
file_path: promptsource/promptsource/session.py
imports: from streamlit.hashing import _CodeHasher
  from streamlit.report_thread import get_report_ctx
  from streamlit.server.server import Server
label_desc: Use image node_id 2 for calling the _SessionState obj's underlying member method code with example usage: obj.__call__() without return types