code: def _apply(self, fn):
      ret = super(QuantRNNBase, self)._apply(fn)
      self.flatten_parameters()
      return ret
  
imports: import math
  import torch
  import warnings
  import itertools
  import numbers
  from torch import nn
  from torch.nn import Parameter
  from torch.nn.utils.rnn import PackedSequence
  from csrc.pytorch.pytorch_quantization import tensor_quant
  from csrc.pytorch.pytorch_quantization.nn._functions import quant_rnn
  from .None import _utils
label_desc: Use image node_id 3 for calling the QuantRNNBase obj's underlying member method code with example usage: obj._apply(fn) and returns: ret