Here is something important to remember when designing systems andinterfaces: users are lazy . Worse, not only are users lazy butthey're very good at detecting pointless work.

What is pointless work? Simple: it's work that the user doesn't see anyvisible benefit from performing (or doesn't understand the benefit andso discounts it, or feels that the benefit is a lot smaller than you'remaking it out to be). Of course, the work is not pointless to you

A long time ago, I wrote some stuff on how generators are not lists (okay, technically it was about iterators), andone of the things that I mentioned is that generators do not havelist methods. Well, there's a consequence of that that only struck merecently: you need completely different code to modify a returnedgenerator than to modify a returned list .

Suppose you have a function that returns something that is conceptuallya list of items. Further suppose that you have another function thatmodifies what