class_docstr: Base class for overriding backward function of quantization operation.
code: def backward(cls, ctx, grad_output):
      (
          tensor,
          quant_type,
          scale,
          zero_point,
          qmin,
          qmax,
      ) = ctx.saved_variables
      output = cls.quant_backward(
          tensor, grad_output, quant_type, scale, zero_point, qmin, qmax
      )
      return output, None, None, None
  
imports: import types
  import logging
  import torch
  from .None import default_layers
label_desc: Use image node_id 5 for calling the QuantGrad obj's underlying member method code with example usage: obj.backward(cls, ctx, grad_output) and returns: output,  None,  None,  None