Find number of non-zero elements in a tensor along an aixs

I want to find the number of non-zero elements in a tensor along a particular axis. Is there any PyTorch function which can do this?

I tried to use the nonzero() method in PyTorch.

torch.nonzero(losses).size(0)

Here, lossess is a tensor of shape 64 x 1. When I run the above statement, it gives me the following error.

TypeError: Type Variable doesn't implement stateless method nonzero

But if I run, torch.nonzero(losses.data).size(0), then it works fine. Any clue, why this is happening or what the error means?