docs: def getCommentByID(self, comment_id):
          """Get the :class:`rtcclient.models.Comment` object by its id
  
          Note: the comment id starts from 0
  
          :param comment_id: the comment id (integer or equivalent string)
          :return: the :class:`rtcclient.models.Comment` object
          :rtype: rtcclient.models.Comment
          """
  
          # check the validity of comment id
          try:
              if isinstance(comment_id, bool):
                  raise ValueError()
              if isinstance(comment_id, six.string_types):
                  comment_id = int(comment_id)
              if not isinstance(comment_id, int):
                  raise ValueError()
          except (ValueError, TypeError):
              raise exception.BadValue("Please input valid comment id")
  
          comment_url = "/".join([self.url,
                                  "rtc_cm:comments/%s" % comment_id])
          try:
              return Comment(comment_url,
                             self.rtc_obj)
          except HTTPError:
              self.log.error("Comment %s does not exist", comment_id)
              raise exception.BadValue("Comment %s does not exist" % comment_id)