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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_refs(self, subspace='', number=-1, etag=None):
 """Iterates over references for this repository. :param str subspace: (optional), e.g. 'tags', 'stashes', 'notes' :param int number: (optional), number of refs to return. Default: -1 returns all available refs :param str etag: (optional), ETag from a previous request to the same endpoint :returns: generator of :class:`Reference <github3.git.Reference>`\ s """

        if subspace:
            args = ('git', 'refs', subspace)
        else:
            args = ('git', 'refs')
        url = self._build_url(*args, base_url=self._api)
        return self._iter(int(number), url, Reference, etag=etag)