[docs] [issue8824] Improve documentation of exec

Terry J. Reedy added the comment:

I suggested more change here than I committed in #13557. I would like to think about the extra a bit more. The issue about def in exec just came up again on python-list, but I do not really like the third sentence I suggested.

---------- assignee: docs@python -> terry.reedy

_______________________________________ Python tracker report@bugs.python.org http://bugs.python.org/issue8824 _______________________________________