In my exams, I try hard to uncover what students’ current mental models are and have an opportunity to review them as necessary.  Although I know it’s unpopular among many, I have them write code on paper as well as solve mechanical code reading problems (Stuart is my hero and I steal all my ideas from him).  Reading their solutions is so eye-opening for me, especially since I can correlate with what I’ve seen them do at the computer.

I recently had my Creative Computing students take a Python quiz.  I asked them a fairly simple conditional problem to get them to define a function that takes parameters and check their conditional syntax.  Something interesting came out.  Here’s the problem:

Write a function choose_todo that takes two parameters: a temperature and a mood.  It should print what to do according to the following rules:

Ok, not particularly demanding or intellectually stimulating but the average and good students did this:

def choose_todo(temp, mood):
    if(temperature >= 60 and mood == "happy"):
        print "Go hiking"
    if(temperature >= 60 and mood == "sad"):
        print "Go fishing"
    if(temperature < 60 and mood == "happy"):
        print "Go hiking"
    if(temperature < 60 and mood == "sad"):
        print "Stay home"

And from EVERY exceptional student, we have:

def choose_todo(temp, mood):
    if(mood == "happy"):
        print "Go hiking"
    else:
        if(temp >= 60):
            print "Go fishing"
        else:
            print "Stay home"

I had the two happy cases be the same to see if they would recognize it, but I didn’t expect it to be such a black and white thing.  I pretty much could give this one problem and assign grades for the year.

The strong students somehow turned the problem around in their brain a bit more before starting to write than the others did.  Of course, the first solution isn’t wrong, it’s just… less satisfying?

This is not by any stretch of the imagination a skill that I explicitly taught.  I showed examples of concise code and discussed the advantages of making mutually exclusive options obviously so by favoring elif/else constructs over sequential ifs… but it was parenthetical at best.  Why do some people just ‘get it?’