Eventually, this should be configured, rather than hardcoded

def build_callbacks(self):
        '''Eventually, this should be configured, rather than hardcoded'''
        # checkpoint
        filepath = os.path.join(CHECKPOINT_DIR, 'weights.best.hdf5')
        checkpoint = ModelCheckpoint(filepath, monitor='val_loss', verbose=1, save_best_only=True, mode='auto')
                                
                                
        self.callbacks = [checkpoint]