Confusing example in "Copy-view behaviour and mutability"

[eric-wieser]

I find this example very confusing:

This happens when views are combined with mutating operations. This simple example illustrates that:

x = ones(1)
x += 2
y = x   # `y` *may* be a view
y -= 1  # if `y` is a view, this modifies `x`

The semantics of Python mean that y = x always makes y a "view" of x - x is y by definition.

I think the point this example is trying to make is that "if -= operates in place, this modifies x" - but the comments tell a different and incorrect story.

Either that, or the example should include a slice operation of some kind, where the library actually does have an chance to decide whether to make a copy or view.

[rgommers]

Thanks for bringing that up @eric-wieser. "view" here means the numpy/pytorch concept of view, which I think has little to do with Python language semantics.

Either that, or the example should include a slice operation of some kind, where the library actually does have an chance to decide whether to make a copy or view.

That was my first though. Would changing to:

y = x[:]  # `y` *may* be a view on the data of `x`

resolve this confusion?

[eric-wieser]

Yes, that would definitely resolve it. I think the x += 2 can also probably be removed, as there's no way it can be relevant to the point if nothing takes a reference to the original x.

[rgommers]

Done now, thanks @eric-wieser