title: KeyError: 'val_acc'
body: <p>Below are some parameters for the model.fit_generator() function. Theses objects are saved in a list labeled callbacks.     </p>
  
  <pre><code>checkpoint = ModelCheckpoint(
          model_file, 
          monitor= 'val_acc', 
          save_best_only=True)
  
  early_stopping = EarlyStopping(
      monitor='val_loss',
      patience=5,
      verbose=1,
      restore_best_weights=True)
  
  
  tensorboard = TensorBoard(
      log_dir=log_dir,
      batch_size=batch_size,
      update_freq = 'batch')
  
  
  reduce_lr = ReduceLROnPlateau(
      monitor='val_loss',
      patience=5,
      cooldown=2,
      min_lr=0.0000000001,
      verbose=1)
  
  
  #-----------------------------------------------------------------------------------------------------------------#
  callbacks = [checkpoint, reduce_lr, early_stopping, tensorboard]
  </code></pre>
  
  <p>After creating the callback objects and parameters for the objects, I implement the layers and compile(which is not shown because it is irrelevant to the problem I am having). Then I run the model.fit_generator function (which uses the callback arguments above): </p>
  
  <pre><code>history = model.fit_generator(
      train_generator,
      steps_per_epoch = steps_per_epoch,
      epochs=epochs,
      verbose=2,
      callbacks=callbacks,
      validation_data=validation_generator,
      validation_steps=validation_steps,
      class_weight=class_weight)
  </code></pre>
  
  <p>The error that I am getting is: </p>
  
  <pre><code>KeyError: 'val_acc'
  </code></pre>
  
  <p>From my understanding this means that val_acc is not in the list. But it is.. so need help to understanding why I am getting this error. </p>
  
  <p>Edit: </p>
  
  <p>Picture of the result before the error shows..[<a href="https://i.stack.imgur.com/5lheg.png]" rel="nofollow noreferrer">https://i.stack.imgur.com/5lheg.png]</a></p>