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Logging

Supported Loggers

The following are loggers we support:

CometLogger

Log using Comet.ml.

CSVLogger

Log to local file system in yaml and CSV format.

MLFlowLogger

Log using MLflow.

NeptuneLogger

Log using Neptune.

TensorBoardLogger

Log to local file system in TensorBoard format.

WandbLogger

Log using Weights and Biases.

The above loggers will normally plot an additional chart (global_step VS epoch). Depending on the loggers you use, there might be some additional charts too.

By default, Lightning uses TensorBoard logger under the hood, and stores the logs to a directory (by default in lightning_logs/).

from pytorch_lightning import Trainer

# Automatically logs to a directory (by default ``lightning_logs/``)
trainer = Trainer()

To see your logs:

tensorboard --logdir=lightning_logs/

To visualize tensorboard in a jupyter notebook environment, run the following command in a jupyter cell:

%reload_ext tensorboard
%tensorboard --logdir=lightning_logs/

You can also pass a custom Logger to the Trainer.

from pytorch_lightning import loggers as pl_loggers

tb_logger = pl_loggers.TensorBoardLogger(save_dir="logs/")
trainer = Trainer(logger=tb_logger)

Choose from any of the others such as MLflow, Comet, Neptune, WandB, etc.

comet_logger = pl_loggers.CometLogger(save_dir="logs/")
trainer = Trainer(logger=comet_logger)

To use multiple loggers, simply pass in a list or tuple of loggers.

tb_logger = pl_loggers.TensorBoardLogger(save_dir="logs/")
comet_logger = pl_loggers.CometLogger(save_dir="logs/")
trainer = Trainer(logger=[tb_logger, comet_logger])

Note

By default, Lightning logs every 50 steps. Use Trainer flags to Control Logging Frequency.

Note

By default, all loggers log to os.getcwd(). You can change the logging path using Trainer(default_root_dir="/your/path/to/save/checkpoints") without instantiating a logger.


Logging from a LightningModule

Lightning offers automatic log functionalities for logging scalars, or manual logging for anything else.

Automatic Logging

Use the log() method to log from anywhere in a lightning module and callbacks.

def training_step(self, batch, batch_idx):
    self.log("my_metric", x)


# or a dict to get multiple metrics on the same plot if the logger supports it
def training_step(self, batch, batch_idx):
    self.log("performance", {"acc": acc, "recall": recall})

Depending on where the log() method is called, Lightning auto-determines the correct logging mode for you. Of course you can override the default behavior by manually setting the log() parameters.

def training_step(self, batch, batch_idx):
    self.log("my_loss", loss, on_step=True, on_epoch=True, prog_bar=True, logger=True)

The log() method has a few options:

  • on_step: Logs the metric at the current step.

  • on_epoch: Automatically accumulates and logs at the end of the epoch.

  • prog_bar: Logs to the progress bar (Default: False).

  • logger: Logs to the logger like Tensorboard, or any other custom logger passed to the Trainer (Default: True).

  • reduce_fx: Reduction function over step values for end of epoch. Uses torch.mean() by default.

  • enable_graph: If True, will not auto detach the graph.

  • sync_dist: If True, reduces the metric across devices. Use with care as this may lead to a significant communication overhead.

  • sync_dist_group: The DDP group to sync across.

  • add_dataloader_idx: If True, appends the index of the current dataloader to the name (when using multiple dataloaders). If False, user needs to give unique names for each dataloader to not mix the values.

  • batch_size: Current batch size used for accumulating logs logged with on_epoch=True. This will be directly inferred from the loaded batch, but for some data structures you might need to explicitly provide it.

  • rank_zero_only: Whether the value will be logged only on rank 0. This will prevent synchronization which would produce a deadlock as not all processes would perform this log call.

Default behavior of logging in Callback or LightningModule

Hook

on_step

on_epoch

on_train_start, on_train_epoch_start, on_train_epoch_end, training_epoch_end

False

True

on_before_backward, on_after_backward, on_before_optimizer_step, on_before_zero_grad

True

False

on_train_batch_start, on_train_batch_end, training_step, training_step_end

True

False

on_validation_start, on_validation_epoch_start, on_validation_epoch_end, validation_epoch_end

False

True

on_validation_batch_start, on_validation_batch_end, validation_step, validation_step_end

False

True

Note

  • The above config for validation applies for test hooks as well.

  • Setting on_epoch=True will cache all your logged values during the full training epoch and perform a reduction in on_train_epoch_end. We recommend using TorchMetrics, when working with custom reduction.

  • Setting both on_step=True and on_epoch=True will create two keys per metric you log with suffix _step and _epoch respectively. You can refer to these keys e.g. in the monitor argument of ModelCheckpoint or in the graphs plotted to the logger of your choice.

If your work requires to log in an unsupported method, please open an issue with a clear description of why it is blocking you.

Manual Logging Non-Scalar Artifacts

If you want to log anything that is not a scalar, like histograms, text, images, etc., you may need to use the logger object directly.

def training_step(self):
    ...
    # the logger you used (in this case tensorboard)
    tensorboard = self.logger.experiment
    tensorboard.add_image()
    tensorboard.add_histogram(...)
    tensorboard.add_figure(...)

Make a Custom Logger

You can implement your own logger by writing a class that inherits from LightningLoggerBase. Use the rank_zero_experiment() and rank_zero_only() decorators to make sure that only the first process in DDP training creates the experiment and logs the data respectively.

from pytorch_lightning.loggers.base import LightningLoggerBase, rank_zero_experiment
from pytorch_lightning.utilities.distributed import rank_zero_only


class MyLogger(LightningLoggerBase):
    @property
    def name(self):
        return "MyLogger"

    @property
    def version(self):
        # Return the experiment version, int or str.
        return "0.1"

    @rank_zero_only
    def log_hyperparams(self, params):
        # params is an argparse.Namespace
        # your code to record hyperparameters goes here
        pass

    @rank_zero_only
    def log_metrics(self, metrics, step):
        # metrics is a dictionary of metric names and values
        # your code to record metrics goes here
        pass

    @rank_zero_only
    def save(self):
        # Optional. Any code necessary to save logger data goes here
        pass

    @rank_zero_only
    def finalize(self, status):
        # Optional. Any code that needs to be run after training
        # finishes goes here
        pass

If you write a logger that may be useful to others, please send a pull request to add it to Lightning!


Control Logging Frequency

Logging frequency

It may slow down training to log on every single batch. By default, Lightning logs every 50 rows, or 50 training steps. To change this behaviour, set the log_every_n_steps Trainer flag.

k = 10
trainer = Trainer(log_every_n_steps=k)

Log Writing Frequency

Individual logger implementations determine their flushing frequency. For example, on the CSVLogger you can set the flag flush_logs_every_n_steps.


Progress Bar

You can add any metric to the progress bar using log() method, setting prog_bar=True.

def training_step(self, batch, batch_idx):
    self.log("my_loss", loss, prog_bar=True)

You could learn more about progress bars supported by Lightning here.

Modifying the Progress Bar

The progress bar by default already includes the training loss and version number of the experiment if you are using a logger. These defaults can be customized by overriding the get_metrics() hook in your logger.

from pytorch_lightning.callbacks.progress import Tqdm


class CustomProgressBar(Tqdm):
    def get_metrics(self, *args, **kwargs):
        # don't show the version number
        items = super().get_metrics()
        items.pop("v_num", None)
        return items

Configure Console Logging

Lightning logs useful information about the training process and user warnings to the console. You can retrieve the Lightning console logger and change it to your liking. For example, adjust the logging level or redirect output for certain modules to log files:

import logging

# configure logging at the root level of Lightning
logging.getLogger("pytorch_lightning").setLevel(logging.ERROR)

# configure logging on module level, redirect to file
logger = logging.getLogger("pytorch_lightning.core")
logger.addHandler(logging.FileHandler("core.log"))

Read more about custom Python logging here.


Logging Hyperparameters

When training a model, it is useful to know what hyperparams went into that model. When Lightning creates a checkpoint, it stores a key "hyper_parameters" with the hyperparams.

lightning_checkpoint = torch.load(filepath, map_location=lambda storage, loc: storage)
hyperparams = lightning_checkpoint["hyper_parameters"]

Some loggers also allow logging the hyperparams used in the experiment. For instance, when using the TensorBoardLogger, all hyperparams will show in the hparams tab.

Note

If you want to track a metric in the tensorboard hparams tab, log scalars to the key hp_metric. If tracking multiple metrics, initialize TensorBoardLogger with default_hp_metric=False and call log_hyperparams only once with your metric keys and initial values. Subsequent updates can simply be logged to the metric keys. Refer to the examples below for setting up proper hyperparams metrics tracking within the LightningModule.

# Using default_hp_metric
def validation_step(self, batch, batch_idx):
    self.log("hp_metric", some_scalar)


# Using custom or multiple metrics (default_hp_metric=False)
def on_train_start(self):
    self.logger.log_hyperparams(self.hparams, {"hp/metric_1": 0, "hp/metric_2": 0})


def validation_step(self, batch, batch_idx):
    self.log("hp/metric_1", some_scalar_1)
    self.log("hp/metric_2", some_scalar_2)

In the example, using "hp/" as a prefix allows for the metrics to be grouped under “hp” in the tensorboard scalar tab where you can collapse them.


Managing Remote Filesystems

Lightning supports saving logs to a variety of filesystems, including local filesystems and several cloud storage providers.

Check out the Remote Filesystems doc for more info.

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