<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _transform(self, var):
        ''' Rename happens automatically in the base class, so all we need to
        do is unset the original variable in the collection. '''
        self.collection.variables.pop(var.name)
        return var.values