'Extract a subset view of the items via slice style indexing
along each dimension. e.g. A[5:10, :]. Each slice consists of
start_idx:stop_idx:step_size triplets.  If step_size isn\'t specified it
defaults to 1.  If start_idx isn\'t specified it defaults to 0.  If
stop_idx isn\'t specified it defaults to the total number of elements
along that dimension.  As such a slice value of \':\' allows one to
select all elements along that dimension.
Arguments:
index (int, slice, tuple): indices of each dimension\'s slice.
Returns:
Tensor: view of self corresponding to the subset items.
Raises:
NotImplementedError: Can\'t be instantiated directly.'

def __getitem__(self, index):

    raise NotImplementedError()
