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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_keys(self, number=-1, etag=None):
 """Iterate over the public keys of this user. .. versionadded:: 0.5 :param int number: (optional), number of keys to return. Default: -1 returns all available keys :param str etag: (optional), ETag from a previous request to the same endpoint :returns: generator of :class:`Key <Key>`\ s """

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