From the chapter, accumulation of a recursive data structure by use of a Queue.
| Q = [[2,1,9],3,[[6,7],0]] |
| def loopsum(List): |
| Accum, Queue = 0, List[:] |
| # Queue starts out with all items |
| while len(Queue)>0: |
| head=Queue.pop(0) |
| if type(head)==int: |
| Accum += head |
| else: # head is a list |
| # move nested items to end |
| Queue.extend(head) |
| # Magically, when loop ends, done! |
| return Accum |
| print loopsum(Q) |