```
@qml.qnode(dev)
def circuit(weights, angles):
statepreparation(angles)
for W in weights:
layer(W)
return qml.expval(qml.PauliZ(0))
def variational_classifier(weights, bias, angles):
return circuit(weights, angles) + bias
def cost(weights, bias, features, labels):
predictions = [variational_classifier(weights, bias, f) for f in features]
return square_loss(labels, predictions)
num_qubits = qbits
num_layers = 6
weights_init = 0.01 * np.random.randn(num_layers, num_qubits, 3, requires_grad=True)
bias_init = np.array(0.0, requires_grad=True)
opt = qml.QNGOptimizer(0.02)
batch_size = 5
# train the variational classifier
weights = weights_init
bias = bias_init
his_acc_val = []
his_acc_train = []
his_cost = []
#cost(weights, bias, features, labels)
for it in range(60):
metric_fn = lambda p: qml.metric_tensor(cost, approx="block-diag")(p, bias, feats_train_batch, Y_train_batch)
# Update the weights by one optimizer step
batch_index = np.random.randint(0, num_train, (batch_size,))
feats_train_batch = feats_train[batch_index]
Y_train_batch = Y_train[batch_index]
weights, bias, _, _ = opt.step(cost, weights, metric_tensor_fn=metric_fn, bias, feats_train_batch, Y_train_batch)
# Compute predictions on train and validation set
predictions_train = [np.sign(variational_classifier(weights, bias, f)) for f in feats_train]
predictions_val = [np.sign(variational_classifier(weights, bias, f)) for f in feats_val]
# Compute accuracy on train and validation set
acc_train = accuracy(Y_train, predictions_train)
acc_val = accuracy(Y_val, predictions_val)
his_acc_val.append(acc_val)
his_acc_train.append(acc_train)
his_cost.append(cost(weights, bias, features, Y))
print(
"Iter: {:5d} | Cost: {:0.7f} | Acc train: {:0.7f} | Acc validation: {:0.7f} "
"".format(it + 1, cost(weights, bias, features, Y), acc_train, acc_val)
)
print(his_acc_val, his_acc_train)
```

Input In [155]

weights, bias, _, _ = opt.step(cost, weights, metric_tensor_fn=metric_fn, bias, feats_train_batch, Y_train_batch)

^

SyntaxError: positional argument follows keyword argument