'Args:
hist_len (int): total length of the state, including the current
and `hist_len-1` history.'

def __init__(self, player, hist_len):

    super(HistoryFramePlayer, self).__init__(player)
    self.history = HistoryBuffer(hist_len, 2)
    s = self.player.current_state()
    self.history.push(s)
