<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def super(self, name, current):
 """Render a parent block."""

        try:
            blocks = self.blocks[name]
            index = blocks.index(current) + 1
            blocks[index]
        except LookupError:
            return self.environment.undefined('there is no parent block '
                                              'called %r.' % name,
                                              name='super')
        return BlockReference(name, self, blocks, index)