class_docstr: Displays a Qt calendar whose date is specified by a 'format' option.
  
  ============== ========================================================
  **Options:**
  format         Format for displaying the date and converting from a string. Can be any value accepted by
                 `QDate.toString` and `fromString`, or a stringified version of a QDateFormat enum, i.e. 'ISODate',
                 'TextDate' (default), etc.
  ============== ========================================================
code: def saveState(self, filter=None):
      state = super().saveState(filter)
      fmt = self._interpretFormat()
      if state["value"] is not None:
          state["value"] = state["value"].toString(fmt)
      return state
  
file_path: pyqtgraph/pyqtgraph/parametertree/parameterTypes/calendar.py
imports: from ...Qt import QtCore, QtWidgets
  from ..Parameter import Parameter
  from .basetypes import WidgetParameterItem
label_desc: Use image node_id 4 for calling the CalendarParameter obj's underlying member method code with example usage: obj.saveState(filter) and returns: state