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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 schema_key_for(self, seq_no: int) -> SchemaKey: """ Get schema key for schema by sequence number if known, None for no such schema in cache. :param seq_no: sequence number :return: corresponding schema key or None """


        LOGGER.debug('SchemaCache.schema_key_for >>> seq_no: %s', seq_no)

        rv = self._seq_no2schema_key.get(seq_no, None)

        LOGGER.debug('SchemaCache.schema_key_for <<< %s', rv)
        return rv