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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 super(self):
 """Super the block."""

        if self._depth + 1 >= len(self._stack):
            return self._context.environment. \
                undefined('there is no parent block called %r.' %
                          self.name, name='super')
        return BlockReference(self.name, self._context, self._stack,
                              self._depth + 1)