In a message of Mon, 09 Nov 2009 12:37:05 +0100, Antoine Pitrou writes:

Le lundi 09 novembre 2009 à 09:17 +0100, Laura Creighton a écrit :

...

The conclusion is that 'surprising' people with unexpected warnings is less useful than one would think -- people tend to overlook them, and thus not be surprised.

Whether or not it's "less useful than one would think" doesn't make it useless. There are many things which fall under the former predicate and not under the latter. For example documentation (many people don't read it), unit tests (they give a false sense of security)... do you suggest we drop them too?

Ok, I was not strong enough. Here is what I believe: Take some sample set of 2000 programs, all of which use features which are scheduled to be deprecated. Divide them into two groups of 1000. In group A you issue DeprecationWarnings for one whole release before the one where this code will break, unless the programmer explicitly turns them off. In group B you don't issue any warnings unless the programmer asks for them. Come the day when /env/python now points to the new release, which group do you believe will have done a better job of modernising their programs? My belief is that this will be group B. I think that the number of programmers in group A who no longer saw the warnings because they were always there will greatly outnumber the ones who never run their programs with warnings turned on, and thus were completely unaware of the problem in the first place. But I am making some assumptions here -- one is that these programs will be run fairly frequently. The second assumption is that the number of programs for whom the fix will be 'change the first line to #! /usr/bin/env/some-older-version-of-python' is small. I don't know if those are decent assumptions to make. I don't have anything approaching real data as to how Python programs exist out there in the world. The "does providing Deprecation Warnings when unasked for actually help" experiement would be interesting to run. This is the sort of thing we need real numbers for, but I haven't seen any experiments to test this so far. All I have seen is indications from cognative psychology that it is really hard for people to see things when they are concentrating on something else. For instance there is the test here http://viscog.beckman.illinois.edu/media/dailytelegraph.html 'view the basketball video' which is explained here: http://www.scholarpedia.org/article/Inattentional_blindness I think that we have two things to worry about here, inattentional blindness (which is what the video tests) and problems caused by insufficient attention (as opposed to inattention). And, links that I posted before which say that people really only see what they expect, rather than what is there, and that our brains are heavily optimised for 'ignoring stuff that doesn't matter' which gets in the way of us noticing stuff that does matter. Unless we expect this. Laura