docs: def participants(self):
          """agents + computers (i.e. all non-observers)"""
          ret = []
          for p in self.players:
              try:
                  if     p.isComputer: ret.append(p)
                  if not p.isObserver: ret.append(p) # could cause an exception if player isn't a PlayerPreGame
              except AttributeError: pass
          return ret