docs: def addlast(self, item, new_priority=None):
          """Adds item to DEPQ as lowest priority. The default
          starting priority is 0, the default new priority is
          self.low(). Performance: O(1)"""
  
          with self.lock:
  
              self_data = self.data
              maxlen = self._maxlen
  
              if maxlen is not None and maxlen == len(self_data):
                  return
  
              try:
                  priority = self_data[-1][1]
                  if new_priority is not None:
                      if new_priority > priority:
                          raise ValueError('Priority must be <= '
                                           'lowest priority.')
                      else:
                          priority = new_priority
              except IndexError:
                  priority = 0 if new_priority is None else new_priority
  
              self_data.append((item, priority))
              self_items = self.items
  
              try:
                  self_items[item] += 1
              except TypeError:
                  self_items[repr(item)] += 1