code: def key(self, frame):
          "Return the sort key for the given frame."
          def keytuple(primary):
              if frame.frameno is None:
                  return (primary, 1)
              return (primary, 0, frame.frameno)
          if type(frame) in self.frame_keys:
              return keytuple(self.frame_keys[type(frame)])
          if frame._in_version(2) and type(frame).__bases__[0] in self.frame_keys:
              return keytuple(self.frame_keys[type(frame).__bases__[0]])
          for (pattern, key) in self.re_keys:
              if re.match(pattern, frame.frameid):
                  return keytuple(key)
          return keytuple(self.unknown_key)