code: def _add_warp_ctc_loss(pred, seq_len, num_label, label):
      
      label = mx.sym.Reshape(data=label, shape=(-1,))
      label = mx.sym.Cast(data=label, dtype='int32')
      return mx.sym.WarpCTC(data=pred, label=label, label_length=num_label, input_length=seq_len)
docs: Adds Symbol.contrib.ctc_loss on top of pred symbol and returns the resulting symbol