class_docstr: Defines a common interface of episodic replay buffer.
  
  Episodic replay buffers allows you to append and sample episodes.
class_docstr_tok: ["Defines","a","common","interface","of","episodic","replay","buffer",".","Episodic","replay","buffers","allows","you","to","append","and","sample","episodes","."]
docstr: Returns the number of episodes in the buffer.
  
  Returns:
      Number of episodes in the buffer.
docstr_tok: ["Returns","the","number","of","episodes","in","the","buffer",".","Returns",":","Number","of","episodes","in","the","buffer","."]
code: def n_episodes(self):
      """Returns the number of episodes in the buffer.
  
      Returns:
          Number of episodes in the buffer.
      """
      raise NotImplementedError
  
imports: from abc import ABCMeta, abstractmethod, abstractproperty
  from typing import Optional
  import numpy
  import torch
  from pfrl.utils.batch_states import batch_states
  from pfrl.utils.recurrent import concatenate_recurrent_states, flatten_sequences_time_first, recurrent_state_from_numpy
label_desc: Use image node_id 2 for calling the AbstractEpisodicReplayBuffer obj's underlying member method code with example usage: obj.n_episodes() without return types