Logging Training and Validation Metrics in PyTorch Lightning

What will you learn?

In this tutorial, you will master the art of visualizing training and validation metrics concurrently using PyTorch Lightning. This skill will enable you to effortlessly monitor your model’s performance as it evolves over time.

Introduction to the Problem and Solution

When delving into the realm of machine learning models, especially neural networks within frameworks like PyTorch Lightning, one crucial aspect is the ability to track and visualize the model’s performance during training. It is imperative to observe how both training and validation metrics progress across epochs. This practice aids in understanding whether the model is learning effectively, detecting signs of overfitting or underfitting, and gauging its rate of improvement.

To address this need in PyTorch Lightning version 2.2.0, we will delve into logging both training and validation metrics onto a unified plot for seamless visualization. Leveraging PyTorch Lightning�s built-in logging functionalities alongside popular visualization tools such as TensorBoard allows us to efficiently achieve this objective. Our solution entails customizing the LightningModule methods to ensure that all essential metrics are appropriately logged during each phase of training.


from pytorch_lightning import LightningModule

class MyModel(LightningModule):
    def __init__(self):
        # Define your model architecture here

    def training_step(self, batch, batch_idx):
        # Perform forward pass & loss calculation here
        loss = ...

        # Log training loss
        self.log('train_loss', loss)

        return loss

    def validation_step(self, batch, batch_idx):
        # Perform forward pass & loss calculation here for validation set
        val_loss = ...

        # Log validation loss
        self.log('val_loss', val_loss)

# Copyright PHD


  • Defining a Model: Within MyModel, inheriting from LightningModule, we define our neural network’s architecture.

  • Logging Training Metrics: In the training_step method, after computing the train loss or any other metric, we utilize self.log(‘train_loss’, loss) where ‘train_loss’ acts as a user-defined tag for identifying specific metrics within logs.

  • Logging Validation Metrics: Similarly in validation_step, post calculating validation set losses or metrics (val_loss), they are logged using self.log(‘val_loss’, val_loss).

By incorporating these logging statements within their respective steps (training_step for processing an epoch of training data and ‘validation_step’ for processing an epoch of validation data), we ensure that these pivotal performance indicators are recorded at every step or epoch throughout our model’s learning journey.

These logged values can be observed through real-time graphs via integrated tools like TensorBoard by running them alongside our code execution: offering immediate visual feedback on our model�s performance progression�across both seen (training) and unseen (validation) data�enabling prompt insights into potential adjustments needed for enhancing performance.

  1. How do I view my logs in TensorBoard?

  2. After logging your data as shown above run tensorboard by pointing it at your log directory:

  3. tensorboard --logdir=your_log_directory_path 
  4. # Copyright PHD
  5. This command initiates TensorBoard which can be accessed through any web browser by visiting the displayed URL.

  6. Can I log additional metrics besides just losses?

  7. Certainly! You can log numerous additional metrics such as accuracy or precision using similar syntax:

  8. self.log('metric_name', metric_value)
  9. # Copyright PHD
  10. What happens if I forget to call self.log()?

  11. If specific metrics are not logged inside their respective steps utilizing self.log(), those particular statistics won’t be tracked nor visible on TensorBoard or any other chosen logger.

  12. Do I need separate functions for different phases like test?

  13. Yes. Analogous functions exist for testing (test_step) where analogous actions tailored towards evaluating your model against test datasets would be performed.

  14. How often does logging occur?

  15. Logging transpires every time either a training_step, ‘validation_step’ or ‘test_step’ executes based on batches processed through those routines – furnishing detailed insight into per-batch/per-step performances.


By diligently implementing consistent metric tracking within our PyTorch Lightning projects via .log() calls; not only do we gain invaluable continuous insights into ongoing developmental experiments but also empower ourselves towards more informed decision-making processes leveraging real-time feedback loops facilitating iterative improvement cycles much more effectively than would otherwise be feasible without such capabilities ultimately driving enhanced outcomes across varied endeavors undertaken therein .

Leave a Comment