On Fri, Oct 27, 2017 at 9:16 AM, Benjamin Root <ben.v.root@gmail.com> wrote:
>
> In what way does it not work? Does it error out at the `arr = arr[mask]` step? Or is it that something unexpected happens?
>
> I am guessing that you are trying to mutate the px, py, pz, w, x, y, z arrays? If so, that for-loop won't do it. In python, a plain simple assignment merely makes the variable point to a different object. It doesn't mutate the object itself.

More specifically, it makes the name on the left-hand side point to the object that's evaluated by the right-hand side. So this for loop is just re-assigning objects to the name "arr". The names "px", "py", etc. are not being reassigned. Here is a good article on how Python assignment works: