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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_transaction_isolation(self):
 """Returns the currently active transaction isolation level. :return: the current transaction isolation level :rtype: int """

        if self._transaction_isolation_level is None:
            self._transaction_isolation_level = self._platform.get_default_transaction_isolation_level()
        return self._transaction_isolation_level