class_docstr: State manager for groups of widgets.
  
  WidgetGroup handles common problems that arise when dealing with groups of widgets like a control
  panel:
  - Provide a single place for saving / restoring the state of all widgets in the group
  - Provide a single signal for detecting when any of the widgets have changed
code: def widgetChanged(self, *args):
      w = self.sender()
      n = self.widgetList[w]
      v1 = self.cache[n]
      v2 = self.readWidget(w)
      if v1 != v2:
          self.sigChanged.emit(self.widgetList[w], v2)
  
imports: import inspect
  import weakref
  from .Qt import QtCore, QtWidgets
label_desc: Use image node_id 9 for calling the WidgetGroup obj's underlying member method code with example usage: obj.widgetChanged() without return types