Keras

Keras callbacks

W&B has three callbacks for Keras, available from wandb v0.13.4. For the legacy WandbCallback scroll down.

• WandbMetricsLogger : Use this callback for Experiment Tracking. It logs your training and validation metrics along with system metrics to W&B.

• WandbModelCheckpoint : Use this callback to log your model checkpoints to W&B Artifacts.

• WandbEvalCallback: This base callback logs model predictions to W&B Tables for interactive visualization.

These new callbacks:

• Adhere to Keras design philosophy.
• Reduce the cognitive load of using a single callback (WandbCallback) for everything.
• Make it easy for Keras users to modify the callback by subclassing it to support their niche use case.

Track experiments with WandbMetricsLogger

WandbMetricsLogger automatically logs Keras’ logs dictionary that callback methods such as on_epoch_end, on_batch_end etc, take as an argument.

This tracks:

• Training and validation metrics defined in model.compile.
• System (CPU/GPU/TPU) metrics.
• Learning rate (both for a fixed value or a learning rate scheduler.

import wandb
from wandb.integration.keras import WandbMetricsLogger

# Initialize a new W&B Run
wandb.init(config={"bs": 12})

# Pass the WandbMetricsLogger to model.fit
model.fit(
    X_train, y_train, validation_data=(X_test, y_test), callbacks=[WandbMetricsLogger()]
)

WandbMetricsLogger reference

Parameter	Description
log_freq	(epoch, batch, or an int): if epoch, logs metrics at the end of each epoch. If batch, logs metrics at the end of each batch. If an int, logs metrics at the end of that many batches. Defaults to epoch.
initial_global_step	(int): Use this argument to correctly log the learning rate when you resume training from some initial_epoch, and a learning rate scheduler is used. This can be computed as step_size * initial_step. Defaults to 0.

Checkpoint a model using WandbModelCheckpoint

Use WandbModelCheckpoint callback to save the Keras model (SavedModel format) or model weights periodically and uploads them to W&B as a wandb.Artifact for model versioning.

This callback is subclassed from tf.keras.callbacks.ModelCheckpoint ,thus the checkpointing logic is taken care of by the parent callback.

This callback saves:

• The model that has achieved best performance based on the monitor.
• The model at the end of every epoch regardless of the performance.
• The model at the end of the epoch or after a fixed number of training batches.
• Only model weights or the whole model.
• The model either in SavedModel format or in .h5 format.

Use this callback in conjunction with WandbMetricsLogger.

import wandb
from wandb.integration.keras import WandbMetricsLogger, WandbModelCheckpoint

# Initialize a new W&B Run
wandb.init(config={"bs": 12})

# Pass the WandbModelCheckpoint to model.fit
model.fit(
    X_train,
    y_train,
    validation_data=(X_test, y_test),
    callbacks=[
        WandbMetricsLogger(),
        WandbModelCheckpoint("models"),
    ],
)

WandbModelCheckpoint reference

Parameter	Description
filepath	(str): path to save the mode file.
monitor	(str): The metric name to monitor.
verbose	(int): Verbosity mode, 0 or 1. Mode 0 is silent, and mode 1 displays messages when the callback takes an action.
save_best_only	(Boolean): if save_best_only=True, it only saves the latest model or the model it considers the best, according to the defined by the monitor and mode attributes.
save_weights_only	(Boolean): if True, saves only the model’s weights.
mode	(auto, min, or max): For val_acc, set it to max, for val_loss, set it to min, and so on
save_freq	(“epoch” or int): When using ‘epoch’, the callback saves the model after each epoch. When using an integer, the callback saves the model at end of this many batches. Note that when monitoring validation metrics such as val_acc or val_loss, save_freq must be set to “epoch” as those metrics are only available at the end of an epoch.
options	(str): Optional tf.train.CheckpointOptions object if save_weights_only is true or optional tf.saved_model.SaveOptions object if save_weights_only is false.
initial_value_threshold	(float): Floating point initial “best” value of the metric to be monitored.

Log checkpoints after N epochs

By default (save_freq="epoch"), the callback creates a checkpoint and uploads it as an artifact after each epoch. To create a checkpoint after a specific number of batches, set save_freq to an integer. To checkpoint after N epochs, compute the cardinality of the train dataloader and pass it to save_freq:

WandbModelCheckpoint(
    filepath="models/",
    save_freq=int((trainloader.cardinality()*N).numpy())
)

Efficiently log checkpoints on a TPU architecture

While checkpointing on TPUs you might encounter UnimplementedError: File system scheme '[local]' not implemented error message. This happens because the model directory (filepath) must use a cloud storage bucket path (gs://bucket-name/...), and this bucket must be accessible from the TPU server. We can however, use the local path for checkpointing which in turn is uploaded as an Artifacts.

checkpoint_options = tf.saved_model.SaveOptions(experimental_io_device="/job:localhost")

WandbModelCheckpoint(
    filepath="models/,
    options=checkpoint_options,
)

Visualize model predictions using WandbEvalCallback

The WandbEvalCallback is an abstract base class to build Keras callbacks primarily for model prediction and, secondarily, dataset visualization.

This abstract callback is agnostic with respect to the dataset and the task. To use this, inherit from this base WandbEvalCallback callback class and implement the add_ground_truth and add_model_prediction methods.

The WandbEvalCallback is a utility class that provides methods to:

• Create data and prediction wandb.Table instances.
• Log data and prediction Tables as wandb.Artifact.
• Log the data table on_train_begin.
• log the prediction table on_epoch_end.

The following example uses WandbClfEvalCallback for an image classification task. This example callback logs the validation data (data_table) to W&B, performs inference, and logs the prediction (pred_table) to W&B at the end of every epoch.

import wandb
from wandb.integration.keras import WandbMetricsLogger, WandbEvalCallback


# Implement your model prediction visualization callback
class WandbClfEvalCallback(WandbEvalCallback):
    def __init__(
        self, validation_data, data_table_columns, pred_table_columns, num_samples=100
    ):
        super().__init__(data_table_columns, pred_table_columns)

        self.x = validation_data[0]
        self.y = validation_data[1]

    def add_ground_truth(self, logs=None):
        for idx, (image, label) in enumerate(zip(self.x, self.y)):
            self.data_table.add_data(idx, wandb.Image(image), label)

    def add_model_predictions(self, epoch, logs=None):
        preds = self.model.predict(self.x, verbose=0)
        preds = tf.argmax(preds, axis=-1)

        table_idxs = self.data_table_ref.get_index()

        for idx in table_idxs:
            pred = preds[idx]
            self.pred_table.add_data(
                epoch,
                self.data_table_ref.data[idx][0],
                self.data_table_ref.data[idx][1],
                self.data_table_ref.data[idx][2],
                pred,
            )


# ...

# Initialize a new W&B Run
wandb.init(config={"hyper": "parameter"})

# Add the Callbacks to Model.fit
model.fit(
    X_train,
    y_train,
    validation_data=(X_test, y_test),
    callbacks=[
        WandbMetricsLogger(),
        WandbClfEvalCallback(
            validation_data=(X_test, y_test),
            data_table_columns=["idx", "image", "label"],
            pred_table_columns=["epoch", "idx", "image", "label", "pred"],
        ),
    ],
)

The W&B Artifact page includes Table logs by default, rather than the Workspace page.

WandbEvalCallback reference

Parameter	Description
data_table_columns	(list) List of column names for the data_table
pred_table_columns	(list) List of column names for the pred_table

Memory footprint details

We log the data_table to W&B when the on_train_begin method is invoked. Once it’s uploaded as a W&B Artifact, we get a reference to this table which can be accessed using data_table_ref class variable. The data_table_ref is a 2D list that can be indexed like self.data_table_ref[idx][n], where idx is the row number while n is the column number. Let’s see the usage in the example below.

Customize the callback

You can override the on_train_begin or on_epoch_end methods to have more fine-grained control. If you want to log the samples after N batches, you can implement on_train_batch_end method.

If you are implementing a callback for model prediction visualization by inheriting WandbEvalCallback and something needs to be clarified or fixed, let us know by opening an issue.

WandbCallback [legacy]

Use the W&B library WandbCallback Class to automatically save all the metrics and the loss values tracked in model.fit.

import wandb
from wandb.integration.keras import WandbCallback

wandb.init(config={"hyper": "parameter"})

...  # code to set up your model in Keras

# Pass the callback to model.fit
model.fit(
    X_train, y_train, validation_data=(X_test, y_test), callbacks=[WandbCallback()]
)

You can watch the short video Get Started with Keras and W&B in Less Than a Minute.

For a more detailed video, watch Integrate W&B with Keras. You can review the Colab Jupyter Notebook.

See our example repo for scripts, including a Fashion MNIST example and the W&B Dashboard it generates.

The WandbCallback class supports a wide variety of logging configuration options: specifying a metric to monitor, tracking of weights and gradients, logging of predictions on training_data and validation_data, and more.

Check out the reference documentation for the keras.WandbCallback for full details.

The WandbCallback

• Automatically logs history data from any metrics collected by Keras: loss and anything passed into keras_model.compile().
• Sets summary metrics for the run associated with the “best” training step, as defined by the monitor and mode attributes. This defaults to the epoch with the minimum val_loss. WandbCallback by default saves the model associated with the best epoch.
• Optionally logs gradient and parameter histogram.
• Optionally saves training and validation data for wandb to visualize.

WandbCallback reference

Arguments
monitor	(str) name of metric to monitor. Defaults to val_loss.
mode	(str) one of {auto, min, max}. min - save model when monitor is minimized max - save model when monitor is maximized auto - try to guess when to save the model (default).
save_model	True - save a model when monitor beats all previous epochs False - don’t save models
save_graph	(boolean) if True save model graph to wandb (default to True).
save_weights_only	(boolean) if True, saves only the model’s weights(model.save_weights(filepath)). Otherwise, saves the full model).
log_weights	(boolean) if True save histograms of the model’s layer’s weights.
log_gradients	(boolean) if True log histograms of the training gradients
training_data	(tuple) Same format (X,y) as passed to model.fit. This is needed for calculating gradients - this is mandatory if log_gradients is True.
validation_data	(tuple) Same format (X,y) as passed to model.fit. A set of data for wandb to visualize. If you set this field, every epoch, wandb makes a small number of predictions and saves the results for later visualization.
generator	(generator) a generator that returns validation data for wandb to visualize. This generator should return tuples (X,y). Either validate_data or generator should be set for wandb to visualize specific data examples.
validation_steps	(int) if validation_data is a generator, how many steps to run the generator for the full validation set.
labels	(list) If you are visualizing your data with wandb this list of labels converts numeric output to understandable string if you are building a classifier with multiple classes. For a binary classifier, you can pass in a list of two labels [label for false, label for true]. If validate_data and generator are both false, this does nothing.
predictions	(int) the number of predictions to make for visualization each epoch, max is 100.
input_type	(string) type of the model input to help visualization. can be one of: (image, images, segmentation_mask).
output_type	(string) type of the model output to help visualziation. can be one of: (image, images, segmentation_mask).
log_evaluation	(boolean) if True, save a Table containing validation data and the model’s predictions at each epoch. See validation_indexes, validation_row_processor, and output_row_processor for additional details.
class_colors	([float, float, float]) if the input or output is a segmentation mask, an array containing an rgb tuple (range 0-1) for each class.
log_batch_frequency	(integer) if None, callback logs every epoch. If set to integer, callback logs training metrics every log_batch_frequency batches.
log_best_prefix	(string) if None, saves no extra summary metrics. If set to a string, prepends the monitored metric and epoch with the prefix and saves the results as summary metrics.
validation_indexes	([wandb.data_types._TableLinkMixin]) an ordered list of index keys to associate with each validation example. If log_evaluation is True and you provide validation_indexes, does not create a Table of validation data. Instead, associates each prediction with the row represented by the TableLinkMixin. To obtain a list of row keys, use Table.get_index() .
validation_row_processor	(Callable) a function to apply to the validation data, commonly used to visualize the data. The function receives an ndx (int) and a row (dict). If your model has a single input, then row["input"] contains the input data for the row. Otherwise, it contains the names of the input slots. If your fit function takes a single target, then row["target"] contains the target data for the row. Otherwise, it contains the names of the output slots. For example, if your input data is a single array, to visualize the data as an Image, provide lambda ndx, row: {"img": wandb.Image(row["input"])} as the processor. Ignored if log_evaluation is False or validation_indexes are present.
output_row_processor	(Callable) same as validation_row_processor, but applied to the model’s output. row["output"] contains the results of the model output.
infer_missing_processors	(Boolean) Determines whether to infer validation_row_processor and output_row_processor if they are missing. Defaults to True. If you provide labels, W&B attempts to infer classification-type processors where appropriate.
log_evaluation_frequency	(int) Determines how often to log evaluation results. Defaults to 0 to log only at the end of training. Set to 1 to log every epoch, 2 to log every other epoch, and so on. Has no effect when log_evaluation is False.

Frequently Asked Questions

How do I use Keras multiprocessing with wandb?

When setting use_multiprocessing=True, this error may occur:

Error("You must call wandb.init() before wandb.config.batch_size")

To work around it:

1. In the Sequence class construction, add: wandb.init(group='...').
2. In main, make sure you’re using if __name__ == "__main__": and put the rest of your script logic inside it.