The attribute .data was deprecated in PyTorch version v0.4.0 (see quoted changelog below), .detach() should be used instead.
.data was the primary way to get the underlying Tensor from a Variable. [...] However, .data can be unsafe in some cases. Any changes on x.data wouldn't be tracked by autograd, and the computed gradients would be incorrect if x is needed in a backward pass.
A safer alternative is to use x.detach(), which also returns a Tensor that shares data with requires_grad=False, but will have its in-place changes reported by autograd if x is needed in backward.
Additionally, .data is not officially documented, whereas .detach() is, and can break in future releases.