On So, 2009-11-15 at 15:12 +0000, Stephen Nelson-Smith wrote: > > To upack your variables a and b you need an iterable object on the right > > side, which returns you exactly 2 variables > > What does 'unpack' mean? I've seen a few Python errors about packing > and unpacking. What does it mean?
Unpacking refers to taking a collection of values and assigning it to a collection of variables. (a,b) = (1,2,3) # this won't work Let's see what it actually means (in pseudo-code): (a,b)[0] = (1,2,3)[0] # a = 1 (a,b)[1] = (1,2,3)[1] # b = 2 (a,b)[2] = (1,2,3)[2] # undefined! = 3 Same goes for the inverse: (a,b,c) = (1,2) # this won't work either in pseudo code: (a,b,c)[0] = (1,2)[0] # a = 1 (a,b,c)[1] = (1,2)[1] # b = 2 (a,b,c)[2] = (1,2)[2] # c = undefined! Basically, just make sure your len(variables) == len(values) before trying to use the unpacking syntax: (a,b,c) = (1,2,3) # this works (a,b) = (1,2) # this works, too Cheers Alan _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
