[docs] [issue17188] Document 'from None' in raise statement doc.

Thomi Richards added the comment: I have attached a patch for 3.4, based on the patch submitted by Nitika Agarwal. The main difference is that I think it's better to be explicit and show a separate example of `raise X from None`. I will submit a patch for later versions as well. ---------- nosy: +thomir Added file: http://bugs.python.org/file44607/issue17188_3.4.patch _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue17188> _______________________________________