Kirby said: > We say "reference" a lot when talking about a variable's relationship > to a piece of memory. I'm thinking "handle" could be used more > (optionally -- this is not an instruction) and we could even show a > coffee cup (doesn't have to be coffee -- a mug) with two handles, when > explaing how two (or more) variables may have the same "contents" (a > feature, but also a source of bugs, confusions for beginners).
Picking a good metaphor, tailored to the pedagogical situation, is very important: it provides the critical cognitive bridge from what the student *already* knows to what you want the student to *learn*. The best metaphor I've encountered for the concept of variable, as implemented by Python, is John Zelle's. On page 34 of "Python Programming: An Introduction to Computer Science", he says: Assigning a variable is like putting one of those little yellow sticky notes on the value and saying, "this is x." Thinking "sticky note" makes it easy to teach students that: * Even if "x" is already assigned to one value, you can assign it to another value. (Take the note off the first value, and stick it onto the second one.) * In Python, any variable can be assigned to any value. (By contrast, some languages have "colored sticky notes", and you can't stick a BLUE sticky note on a RED value). John Z, do you take this angle in your book? I didn't see it, but I confess I may have failed to look thoroughly enough for it! * You can assign "x" and "y" (etc.) to the same value. (You can place any number of sticky notes on the same value. A note is always attached to a value -- a note is never attached to another note.) * Jut what does the "del" statement actually do? (It removes one sticky note from a value. If a value loses all its sticky notes, it becomes totally *incommunicado* -- there's no way to get to the value.) * What's a namespace? (A bunch of sticky notes.) * etc., etc. The coffee-cup-handle metaphor is certainly useful, but IMHO not quite as spot-on as the sticky-note metaphor. -John Posner _______________________________________________ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig
