class FocalLoss(nn.Module):

```
def __init__(self, weight=None,
gamma=2., reduction='none'):
nn.Module.__init__(self)
self.weight = weight
self.gamma = gamma
self.reduction = reduction
def forward(self, input_tensor, target_tensor):
target_tensor = torch.argmax(target_tensor ,axis=1)
log_prob = F.log_softmax(input_tensor, dim=-1)
prob = torch.exp(log_prob)
return F.nll_loss(
((1 - prob) ** self.gamma) * log_prob,
target_tensor,
weight=self.weight,
reduction = self.reduction
)
```

—> 33 batch_loss += loss.item()

34 total_loss += loss.item()

35

ValueError: only one element tensors can be converted to Python scalars