code: def nextClass(self, classuri):
          
          if classuri == self.classes[-1].uri:
              return self.classes[0]
          flag = False
          for x in self.classes:
              if flag == True:
                  return x
              if x.uri == classuri:
                  flag = True
          return None
docs: Returns the next class in the list of classes. If it's the last one, returns the first one.