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Description
The array API specification stipulates that the slicing syntax needs to be equivalent to Pythons slice() syntax. That includes negative step sizes that PyTorch does not support:
import torch
t = torch.rand((3,))
t[::-1]ValueError: step must be greater than zero
Additional context
This was already proposed in #229, but finally dismissed in #229 (comment) in favor of torch.flip(). Note that this is only a substitution for a negative step size of 1 (::-1) rather than negative step sizes in general.