Daniel Voigt Godoy - Deep Learning with PyTorch Step-by-Step A Beginner’s Guide-leanpub

Just like make_train_step_fn(), our new function, make_val_step_fn(), is a
higher-order function. Its code looks like this:
Helper Function #3
1 def make_val_step_fn(model, loss_fn):
2 # Builds function that performs a step
3 # in the validation loop
4 def perform_val_step_fn(x, y):
5 # Sets model to EVAL mode
6 model.eval() 1
7
8 # Step 1 - Computes our model's predicted output
9 # forward pass
10 yhat = model(x)
11 # Step 2 - Computes the loss
12 loss = loss_fn(yhat, y)
13 # There is no need to compute Steps 3 and 4,
14 # since we don't update parameters during evaluation
15 return loss.item()
16
17 return perform_val_step_fn
1 Setting model to evaluation mode
148 | Chapter 2: Rethinking the Training Loop