code: def is_instance(self):
          
          ret = False
          val = self.callback
          if self.is_class(): return False
  
          ret = not inspect.isfunction(val) and not inspect.ismethod(val)
  #         if is_py2:
  #             ret = isinstance(val, types.InstanceType) or hasattr(val, '__dict__') \
  #                 and not (hasattr(val, 'func_name') or hasattr(val, 'im_func'))
  # 
  #         else:
  #             ret = not inspect.isfunction(val) and not inspect.ismethod(val)
  
          return ret
docs: return True if callback is an instance of a class