On Mon, 2006-06-12 at 11:26 -0400, Kermit Rose wrote: > # to insert 3 between 2 and 4 in > > B = [1,2,4,5] > > B.append(B[3:3])
>>> B[3:3] [] >>> B[3:4] [5] >>> B[0:1] [1] >>> B[:2] [1, 2] >>> B.append(B[3:3]) >>> B [1, 2, 4, 5, []] > > # I expected B[4] to have the value 5 at this point. > # It is empty. Why? You appended an empty list. Note that slice notation returns a list, so you would more commonly use B.extend(B[0:3]) to avoid nested lists. The number before the : is the index to include from The number after the : is the index to exclude Slices are half-open intervals. The lower-bound is included while the upper-bound is excluded. http://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF Provides an excellent justification for this approach (cited recently on this list) -- Lloyd Kvam Venix Corp _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
