class_docstr: Stateless recurrent link interface.
  
  This class defines the interface of a recurrent link ChainerRL can handle.
  
  In most casese, you can just use ChainerRL's existing containers like
  `chainerrl.links.StatelessRecurrentChainList`,
  `chainerrl.links.StatelessRecurrentSequential`, and
  `chainerrl.links.StatelessRecurrentBranched` to define a recurrent
  link. You can use Chainer's recurrent links such as L.NStepLSTM inside the
  containers.
  
  To write your own recurrent link, you need to implement the interface.
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docstr: Return a recurrent state masked at given indices.
  
  This method can be used to initialize a recurrent state only for a
  certain sequence, not all the sequences.
  
  Args:
      recurrent_state (object): Batched recurrent state.
      indices (int or array-like of ints): Which recurrent state to mask.
  
  Returns:
      object: New batched recurrent state.
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code: def mask_recurrent_state_at(self, recurrent_state, indices):
      """Return a recurrent state masked at given indices.
  
      This method can be used to initialize a recurrent state only for a
      certain sequence, not all the sequences.
  
      Args:
          recurrent_state (object): Batched recurrent state.
          indices (int or array-like of ints): Which recurrent state to mask.
  
      Returns:
          object: New batched recurrent state.
      """
      raise NotImplementedError
  
imports: from cached_property import cached_property
  import chainer
  import chainer.functions
  import chainer.links
  import numpy
label_desc: Use image node_id 3 for calling the StatelessRecurrent obj's underlying member method code with example usage: obj.mask_recurrent_state_at(recurrent_state, indices) without return types