code: def __init__(self, ctx, pad_width, mode="constant", constant_value=0):
      super(PadDataGrad, self).__init__(ctx)
      self._func = _F.Pad(ctx, pad_width, mode, constant_value)
  
file_path: nnabla/python/src/nnabla/backward_function/pad.py
imports: import nnabla
  import nnabla.function
  import nnabla.functions
  from .backward_function import UnaryDataGrad
label_desc: Use image node_id 1 to create a new PadDataGrad object from inherited base classes: UnaryDataGrad with example: obj = PadDataGrad(ctx, pad_width, mode, constant_value)