code: def require_axis(f):
      
  
      @wraps(f)
      def _wrapper(self, *args, **kwargs):
          if None in (self.axis, self.sel_axis):
              raise ValueError('%(func_name) requires the node %(node)s '
                      'to have an axis and a sel_axis function' %
                      dict(func_name=f.__name__, node=repr(self)))
  
          return f(self, *args, **kwargs)
  
      return _wrapper
docs: Check if the object of the function has axis and sel_axis members