code: def iter_labels(self, number=-1, etag=None):
          
          url = self._build_url('labels', base_url=self._api)
          return self._iter(int(number), url, Label, etag=etag)
docs: 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