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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 _lookup_identity_names(self):
 """ Batch resolve identities to usernames. Returns a dict mapping IDs to Usernames """

        id_batch_size = 100

        # fetch in batches of 100, store in a dict
        ac = get_auth_client()
        self._resolved_map = {}
        for i in range(0, len(self.identity_ids), id_batch_size):
            chunk = self.identity_ids[i : i + id_batch_size]
            resolved_result = ac.get_identities(ids=chunk)
            for x in resolved_result["identities"]:
                self._resolved_map[x["id"]] = x["username"]