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 interface(self, obj):
      t = type(obj)
      if t in WidgetGroup.classes:
          return WidgetGroup.classes[t]
      else:
          return obj.widgetGroupInterface()
  
imports: import inspect
  import weakref
  from .Qt import QtCore, QtWidgets
label_desc: Use image node_id 4 for calling the WidgetGroup obj's underlying member method code with example usage: obj.interface(obj) and returns: WidgetGroup, obj