code: def gradient(self, y, y_pred):
      raise NotImplementedError()
  
file_path: ML-From-Scratch/mlfromscratch/deep_learning/loss_functions.py
imports: from __future__ import division
  import numpy
  from mlfromscratch.utils import accuracy_score
  from mlfromscratch.deep_learning.activation_functions import Sigmoid
label_desc: Use image node_id 2 for calling the Loss obj's underlying member method code with example usage: obj.gradient(y, y_pred) without return types