code: def transforms(self):
          
  
          tr = []
          for c in self.columns:
              tr.append(c.expanded_transform)
  
          return six.moves.zip_longest(*tr)
docs: Return an array of arrays of column transforms.
  
          #The return value is an list of list, with each list being a segment of column transformations, and
          #each segment having one entry per column.