torch.is_nonzero
torch.is_nonzero(input)
Returns True if the "input" is a single element tensor which is not
   equal to zero after type conversions. i.e. not equal to
   "torch.tensor([0.])" or "torch.tensor([0])" or
   "torch.tensor([False])". Throws a "RuntimeError" if "torch.numel()
   != 1" (even in case of sparse tensors).
Parameters:
      input (Tensor) -- the input tensor.
Examples:
  >>> torch.is_nonzero(torch.tensor([0.]))
  False
  >>> torch.is_nonzero(torch.tensor([1.5]))
  True
  >>> torch.is_nonzero(torch.tensor([False]))
  False
  >>> torch.is_nonzero(torch.tensor([3]))
  True
  >>> torch.is_nonzero(torch.tensor([1, 3, 5]))
  Traceback (most recent call last):
  ...
  RuntimeError: bool value of Tensor with more than one value is ambiguous
  >>> torch.is_nonzero(torch.tensor([]))
  Traceback (most recent call last):
  ...
  RuntimeError: bool value of Tensor with no values is ambiguous
