def _add_notifiers(self, handler, name):
        if name not in self._trait_notifiers:
            nlist = []
            self._trait_notifiers[name] = nlist
        else:
            nlist = self._trait_notifiers[name]
        if nlist not in handler:
            nlist.append(handler)
dataset/ETHPy150Open enthought/depsolver/depsolver/bundled/traitlets/_implementation.py/HasTraits._add_notifiers/swapped operands of `not in`