class_docstr: KLDivLoss
code: def _cat_mask(self, t, mask1, mask2):
      t1 = (t * mask1).sum(axis=1, keepdim=True)
      t2 = (t * mask2).sum(axis=1, keepdim=True)
      rt = paddle.concat([t1, t2], axis=1)
      return rt
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.nn import L1Loss
  from paddle.nn import MSELoss
  from paddle.nn import SmoothL1Loss
label_desc: Use image node_id 2 for calling the DKDLoss obj's underlying member method code with example usage: obj._cat_mask(t, mask1, mask2) and returns: rt