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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 commit(self):
 """Commit changes made by the latest session."""

        if self.session is not None:
            logger.info("committing transaction in %s" % self)
            tmp = self.stable
            self.stable, self.session = self.session, None
            self.istable = 1 - self.istable
            self.write_istable()
            tmp.close() # don't wait for gc, release resources manually
            self.lock_update.release()
        else:
            logger.warning("commit called but there's no open session in %s" % self)