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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 _get_matching_dns_entry_ids(self, identifier=None, rtype=None, name=None, content=None):
 """Return a list of DNS entries that match the given criteria."""

        record_ids = []
        if not identifier:
            records = self._list_records(rtype, name, content)
            record_ids = [record['id'] for record in records]
        else:
            record_ids.append(identifier)
        return record_ids