Now I got it, thanks :-) a, b = b, b + a
... I was was wrongly assuming that "a" and "b" on the left side "talk" to each other and that "a" tells "b" something like: "Hey 'b' ... I just assigned another value to you, make sure you execute it." But "a" and "b" don't talk to each other. Each of them executes what it is supposed to and doesn't take notice of what its neighbor variable does. The more sophisticated explanation (from my view point as an absolute beginner who's not familiar with most programming concepts yet) is that "a" and "b" on the left side are unchangable tuples and they simply get unpacked on the right side. I wrote an even more primitive program which helped me understand what *exactly* happens with "a" and "b" with each run: # 1st run a, b = 1, 5 print(a) # 1 print(b) # 5 # 2nd run a, b = b, b + a print(a) # a = b = 5 print(b) # b + a = 5 + 1 = 6 # 3rd run a, b = b, b + a print(a) # a = b = 6 print(b) # b + a = 6 + 5 = 11 # 4th run a, b = b, b + a print(a) # a = b = 11 print(b) # b + a = 11 + 6 = 17 # 5th run a, b = b, b + a print(a) # a = b = 17 print(b) # b + a = 17 + 11 = 28 # 6th run a, b = b, b + a print(a) # a = b = 28 print(b) # b + a = 28 + 17 0 45 All the best, Raf On Sun, Nov 24, 2013 at 12:33 PM, Dave Angel <da...@davea.name> wrote: > On Sun, 24 Nov 2013 11:24:43 +0100, Rafael Knuth <rafael.kn...@gmail.com> > wrote: > >> a, b = b, a +b >> > > > a = b = 1 >> b = a + b = 1 + 1 = 2 >> > > I suggest you play with the statement a bit. Print out both values each > time through the loop. > > The expression b, a+b produces a tuple. The left side a, b *unpacks* that > tuple into the two variables.a and b. > > Perhaps a simpler case might help. Try a, b = b, a What would you expect > it to do and why? > > -- > DaveA > > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor >
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