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"""
Contains functions for training and testing a PyTorch model.
"""
import torch
from tqdm.auto import tqdm
from typing import Dict, List, Tuple
def train_step(model: torch.nn.Module,
dataloader: torch.utils.data.DataLoader,
loss_fn: torch.nn.Module,
optimizer: torch.optim.Optimizer,
device: torch.device) -> Tuple[float, float]:
"""Trains a PyTorch model for a single epoch.
Turns a target PyTorch model to training mode and then
runs through all of the required training steps (forward
pass, loss calculation, optimizer step).
Args:
model: A PyTorch model to be trained.
dataloader: A DataLoader instance for the model to be trained on.
loss_fn: A PyTorch loss function to minimize.
optimizer: A PyTorch optimizer to help minimize the loss function.
device: A target device to compute on (e.g. "cuda" or "cpu").
Returns:
A tuple of training loss and training accuracy metrics.
In the form (train_loss, train_accuracy). For example:
(0.1112, 0.8743)
"""
# Put model in train mode
model.train()
# Setup train loss and train accuracy values
train_loss, train_acc = 0, 0
# Loop through data loader data batches
for batch, (X, y) in enumerate(dataloader):
# Send data to target device
X, y = X.to(device), y.to(device)
# 1. Forward pass
y_pred = model(X)
# 2. Calculate and accumulate loss
loss = loss_fn(y_pred, y)
train_loss += loss.item()
# 3. Optimizer zero grad
optimizer.zero_grad()
# 4. Loss backward
loss.backward()
# 5. Optimizer step
optimizer.step()
# Calculate and accumulate accuracy metric across all batches
y_pred_class = torch.argmax(torch.softmax(y_pred, dim=1), dim=1)
train_acc += (y_pred_class == y).sum().item()/len(y_pred)
# Adjust metrics to get average loss and accuracy per batch
train_loss = train_loss / len(dataloader)
train_acc = train_acc / len(dataloader)
return train_loss, train_acc
def test_step(model: torch.nn.Module,
dataloader: torch.utils.data.DataLoader,
loss_fn: torch.nn.Module,
device: torch.device) -> Tuple[float, float]:
"""Tests a PyTorch model for a single epoch.
Turns a target PyTorch model to "eval" mode and then performs
a forward pass on a testing dataset.
Args:
model: A PyTorch model to be tested.
dataloader: A DataLoader instance for the model to be tested on.
loss_fn: A PyTorch loss function to calculate loss on the test data.
device: A target device to compute on (e.g. "cuda" or "cpu").
Returns:
A tuple of testing loss and testing accuracy metrics.
In the form (test_loss, test_accuracy). For example:
(0.0223, 0.8985)
"""
# Put model in eval mode
model.eval()
# Setup test loss and test accuracy values
test_loss, test_acc = 0, 0
# Turn on inference context manager
with torch.inference_mode():
# Loop through DataLoader batches
for batch, (X, y) in enumerate(dataloader):
# Send data to target device
X, y = X.to(device), y.to(device)
# 1. Forward pass
test_pred_logits = model(X)
# 2. Calculate and accumulate loss
loss = loss_fn(test_pred_logits, y)
test_loss += loss.item()
# Calculate and accumulate accuracy
test_pred_labels = test_pred_logits.argmax(dim=1)
test_acc += ((test_pred_labels == y).sum().item()/len(test_pred_labels))
# Adjust metrics to get average loss and accuracy per batch
test_loss = test_loss / len(dataloader)
test_acc = test_acc / len(dataloader)
return test_loss, test_acc
def train(model: torch.nn.Module,
train_dataloader: torch.utils.data.DataLoader,
test_dataloader: torch.utils.data.DataLoader,
optimizer: torch.optim.Optimizer,
loss_fn: torch.nn.Module,
epochs: int,
device: torch.device) -> Dict[str, List]:
"""Trains and tests a PyTorch model.
Passes a target PyTorch models through train_step() and test_step()
functions for a number of epochs, training and testing the model
in the same epoch loop.
Calculates, prints and stores evaluation metrics throughout.
Args:
model: A PyTorch model to be trained and tested.
train_dataloader: A DataLoader instance for the model to be trained on.
test_dataloader: A DataLoader instance for the model to be tested on.
optimizer: A PyTorch optimizer to help minimize the loss function.
loss_fn: A PyTorch loss function to calculate loss on both datasets.
epochs: An integer indicating how many epochs to train for.
device: A target device to compute on (e.g. "cuda" or "cpu").
Returns:
A dictionary of training and testing loss as well as training and
testing accuracy metrics. Each metric has a value in a list for
each epoch.
In the form: {train_loss: [...],
train_acc: [...],
test_loss: [...],
test_acc: [...]}
For example if training for epochs=2:
{train_loss: [2.0616, 1.0537],
train_acc: [0.3945, 0.3945],
test_loss: [1.2641, 1.5706],
test_acc: [0.3400, 0.2973]}
"""
# Create empty results dictionary
results = {"train_loss": [],
"train_acc": [],
"test_loss": [],
"test_acc": []
}
# Loop through training and testing steps for a number of epochs
for epoch in tqdm(range(epochs)):
train_loss, train_acc = train_step(model=model,
dataloader=train_dataloader,
loss_fn=loss_fn,
optimizer=optimizer,
device=device)
test_loss, test_acc = test_step(model=model,
dataloader=test_dataloader,
loss_fn=loss_fn,
device=device)
# Print out what's happening
print(
f"Epoch: {epoch+1} | "
f"train_loss: {train_loss:.4f} | "
f"train_acc: {train_acc:.4f} | "
f"test_loss: {test_loss:.4f} | "
f"test_acc: {test_acc:.4f}"
"\n"
)
# Update results dictionary
results["train_loss"].append(train_loss)
results["train_acc"].append(train_acc)
results["test_loss"].append(test_loss)
results["test_acc"].append(test_acc)
# Return the filled results at the end of the epochs
return results |