docs: def learn(self, msg, learnas):
          """Learn message as spam/ham or forget"""
          if not isinstance(learnas, types.StringTypes):
              raise SpamCError('The learnas option is invalid')
          if learnas.lower() == 'forget':
              resp = self.tell(msg, 'forget')
          else:
              resp = self.tell(msg, 'learn', learnas)
          return resp