class_docstr: FIFO queue with fast indexing
  
  Operations getitem, setitem, append, popleft, and len
  are amortized O(1)-time, if this data structure is used ephemerally.
code: def append(self, x):
      self._queue_back.append(x)
      if self.maxlen is not None and len(self) > self.maxlen:
          self.popleft()
  
file_path: pfrl/pfrl/collections/random_access_queue.py
imports: import itertools
  from pfrl.utils.random import sample_n_k
label_desc: Use image node_id 8 for calling the RandomAccessQueue obj's underlying member method code with example usage: obj.append(x) without return types