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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def iter_features(self, stanza=None):
 """ Return an iterator which yields the features of the node. :param stanza: The IQ request stanza :type stanza: :class:`~aioxmpp.IQ` :rtype: iterable of :class:`str` :return: :xep:`30` features of this node `stanza` is the :class:`aioxmpp.IQ` stanza of the request. This can be used to filter the list according to who is asking (not recommended). `stanza` may be :data:`None` if the features are queried without a specific request context. In that case, implementors should assume that the result is visible to everybody. .. note:: Subclasses must allow :data:`None` for `stanza` and default it to :data:`None`. The features are returned as strings. The features demanded by :xep:`30` are always returned. """

        return itertools.chain(
            iter(self.STATIC_FEATURES),
            iter(self._features)
        )