code: def _create_variables_pretrain(self):
          
          for l, layer in enumerate(self.layers):
  
              w_name = 'enc-w-{}'.format(l)
              b_name = 'enc-b-{}'.format(l)
  
              self.encoding_w_[l] = tf.Variable(
                  self.encoding_w_[l], name=w_name)
              tf.summary.histogram(w_name, self.encoding_w_[l])
  
              self.encoding_b_[l] = tf.Variable(
                  self.encoding_b_[l], name=b_name)
              tf.summary.histogram(b_name, self.encoding_w_[l])
docs: Create model variables (previous unsupervised pretraining).
  
          :return: self