class_docstr: Class for extracting activations and
  registering gradients from targeted intermediate layers 
code: def __call__(self, x):
      self.gradients = []
      self.activations = []
      return self.model(x)
  
imports: import cv2
  import numpy
label_desc: Use image node_id 4 for calling the ActivationsAndGradients obj's underlying member method code with example usage: obj.__call__(x) and returns: self