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Add W&B (wandb) to your code

There are numerous ways to add the W&B Python SDK to your script or Jupyter Notebook. Outlined below is a "best practice" example of how to integrate the W&B Python SDK into your own code.

Original training script​

Suppose you have the following code in a Jupyter Notebook cell or Python script. We define a function called main that mimics a typical training loop; for each epoch, the accuracy and loss is computed on the training and validation data sets. The values are randomly generated for the purpose of this example.

We defined a dictionary called config where we store hyperparameters values (line 15). At the end of the cell, we call the main function to execute the mock training code.

# train.py
import random
import numpy as np


def train_one_epoch(epoch, lr, bs):
    acc = 0.25 + ((epoch / 30) + (random.random() / 10))
    loss = 0.2 + (1 - ((epoch - 1) / 10 + random.random() / 5))
    return acc, loss


def evaluate_one_epoch(epoch):
    acc = 0.1 + ((epoch / 20) + (random.random() / 10))
    loss = 0.25 + (1 - ((epoch - 1) / 10 + random.random() / 6))
    return acc, loss


config = {"lr": 0.0001, "bs": 16, "epochs": 5}


def main():
    # Note that we define values from `wandb.config`
    # instead of defining hard values
    lr = config["lr"]
    bs = config["bs"]
    epochs = config["epochs"]

    for epoch in np.arange(1, epochs):
        train_acc, train_loss = train_one_epoch(epoch, lr, bs)
        val_acc, val_loss = evaluate_one_epoch(epoch)

        print("epoch: ", epoch)
        print("training accuracy:", train_acc, "training loss:", train_loss)
        print("validation accuracy:", val_acc, "training loss:", val_loss)


# Call the main function.
main()

Training script with W&B Python SDK​

The following code examples demonstrate how to add the W&B Python SDK into your code. If you start W&B Sweep jobs in the CLI, you will want to explore the CLI tab. If you start W&B Sweep jobs within a Jupyter notebook or Python script, explore the Python SDK tab.

To create a W&B Sweep, we added the following to the code example:

  1. Line 1: Import the Weights & Biases Python SDK.
  2. Line 6: Create a dictionary object where the key-value pairs define the sweep configuration. In the proceeding example, the batch size (batch_size), epochs (epochs), and the learning rate (lr) hyperparameters are varied during each sweep. For more information on how to create a sweep configuration, see Define sweep configuration.
  3. Line 19: Pass the sweep configuration dictionary to wandb.sweep. This initializes the sweep. This returns a sweep ID (sweep_id). For more information on how to initialize sweeps, see Initialize sweeps.
  4. Line 33: Use the wandb.init() API to generate a background process to sync and log data as a W&B Run.
  5. Line 37-39: (Optional) define values from wandb.config instead of defining hard coded values.
  6. Line 45: Log the metric we want to optimize with wandb.log. You must log the metric defined in your configuration. Within the configuration dictionary (sweep_configuration in this example) we defined the sweep to maximize the val_acc value).
  7. Line 54: Start the sweep with the wandb.agent API call. Provide the sweep ID (line 19), the name of the function the sweep will execute (function=main), and set the maximum number of runs to try to four (count=4). For more information on how to start W&B Sweep, see Start sweep agents.
import wandb
import numpy as np
import random

# Define sweep config
sweep_configuration = {
    "method": "random",
    "name": "sweep",
    "metric": {"goal": "maximize", "name": "val_acc"},
    "parameters": {
        "batch_size": {"values": [16, 32, 64]},
        "epochs": {"values": [5, 10, 15]},
        "lr": {"max": 0.1, "min": 0.0001},
    },
}

# Initialize sweep by passing in config.
# (Optional) Provide a name of the project.
sweep_id = wandb.sweep(sweep=sweep_configuration, project="my-first-sweep")


# Define training function that takes in hyperparameter
# values from `wandb.config` and uses them to train a
# model and return metric
def train_one_epoch(epoch, lr, bs):
    acc = 0.25 + ((epoch / 30) + (random.random() / 10))
    loss = 0.2 + (1 - ((epoch - 1) / 10 + random.random() / 5))
    return acc, loss


def evaluate_one_epoch(epoch):
    acc = 0.1 + ((epoch / 20) + (random.random() / 10))
    loss = 0.25 + (1 - ((epoch - 1) / 10 + random.random() / 6))
    return acc, loss


def main():
    run = wandb.init()

    # note that we define values from `wandb.config`
    # instead of defining hard values
    lr = wandb.config.lr
    bs = wandb.config.batch_size
    epochs = wandb.config.epochs

    for epoch in np.arange(1, epochs):
        train_acc, train_loss = train_one_epoch(epoch, lr, bs)
        val_acc, val_loss = evaluate_one_epoch(epoch)

        wandb.log(
            {
                "epoch": epoch,
                "train_acc": train_acc,
                "train_loss": train_loss,
                "val_acc": val_acc,
                "val_loss": val_loss,
            }
        )


# Start sweep job.
wandb.agent(sweep_id, function=main, count=4)

Consideration when logging metrics​

Ensure to log the metric you specify in your sweep configuration explicitly to W&B. Do not log metrics for your sweep inside of a sub-directory.

For example, consider the proceeding psuedocode. A user wants to log the validation loss ("val_loss": loss). First they pass the values into a dictionary (line 16). However, the dictionary passed to wandb.log does not explicitly access the key-value pair in the dictionary:

train.py
# Import the W&B Python Library and log into W&B
import wandb
import random


def train():
    offset = random.random() / 5
    acc = 1 - 2**-epoch - random.random() / epoch - offset
    loss = 2**-epoch + random.random() / epoch + offset

    val_metrics = {"val_loss": loss, "val_acc": acc}
    return val_metrics


def main():
    wandb.init(entity="<entity>", project="my-first-sweep")
    val_metrics = train()
    wandb.log({"val_loss": val_metrics})


sweep_configuration = {
    "method": "random",
    "metric": {"goal": "minimize", "name": "val_loss"},
    "parameters": {
        "x": {"max": 0.1, "min": 0.01},
        "y": {"values": [1, 3, 7]},
    },
}

sweep_id = wandb.sweep(sweep=sweep_configuration, project="my-first-sweep")

wandb.agent(sweep_id, function=main, count=10)

Instead, explicitly access the key-value pair within the Python dictionary. For example, the proceeding code (line after you create a dictionary, specify the key-value pair when you pass the dictionary to the wandb.log method:

train.py
# Import the W&B Python Library and log into W&B
import wandb
import random


def train():
    offset = random.random() / 5
    acc = 1 - 2**-epoch - random.random() / epoch - offset
    loss = 2**-epoch + random.random() / epoch + offset

    val_metrics = {"val_loss": loss, "val_acc": acc}
    return val_metrics


def main():
    wandb.init(entity="<entity>", project="my-first-sweep")
    val_metrics = train()
    wandb.log({"val_loss", val_metrics["val_loss"]})


sweep_configuration = {
    "method": "random",
    "metric": {"goal": "minimize", "name": "val_loss"},
    "parameters": {
        "x": {"max": 0.1, "min": 0.01},
        "y": {"values": [1, 3, 7]},
    },
}

sweep_id = wandb.sweep(sweep=sweep_configuration, project="my-first-sweep")

wandb.agent(sweep_id, function=main, count=10)
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