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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_labels(self, number=-1, etag=None):
 """Iterate over the labels for every issue associated with this milestone. .. versionchanged:: 0.9 Add etag parameter. :param int number: (optional), number of labels to return. Default: -1 returns all available labels. :param str etag: (optional), ETag header from a previous response :returns: generator of :class:`Label <github3.issues.label.Label>`\ s """

        url = self._build_url('labels', base_url=self._api)
        return self._iter(int(number), url, Label, etag=etag)