The _replace method returns a new tuple. The existing tuple is not changed. There's no reason not to use that method. It's part of namedtuple's formal API. The

The _replace method returns a new tuple. The existing tuple is not changed. There's no reason not to use that method. It's part of namedtuple's formal API. The reason for the underscore is so that the method name won't collide with a field. (All of namedtuple's methods use a leading underscore.)