Victor Subervi wrote: > Hi; > I have the following code snippet: > > print 'Original: ', catChains, '<br />' > while i < MAXLEVEL: > flag = 0 > j = 0 > while j < len(parents): > for chain in catChains: > if parents[j] == chain[len(chain)-1]: > chain.append(children[j]) > print '1: ', catChains, '<br />' > catChains.append(chain) > print '2: ', catChains, '<br />' > flag = 1 > j += 1 > i += 1 > if flag == 0: > break > print 'Final: ', catChains > > which prints this: > > Original: [['prodCat1'], ['prodCat2']] > 1: [['prodCat1', 'prodCat3'], ['prodCat2']] > 2: [['prodCat1', 'prodCat3'], ['prodCat2'], ['prodCat1', 'prodCat3']] > 1: [['prodCat1', 'prodCat3', 'prodCat5'], ['prodCat2'], ['prodCat1', > 'prodCat3', 'prodCat5']] > 2: [['prodCat1', 'prodCat3', 'prodCat5'], ['prodCat2'], ['prodCat1', > 'prodCat3', 'prodCat5'], ['prodCat1', 'prodCat3', 'prodCat5']] > Final: [['prodCat1', 'prodCat3', 'prodCat5'], ['prodCat2'], ['prodCat1', > 'prodCat3', 'prodCat5'], ['prodCat1', 'prodCat3', 'prodCat5']] > > Why is it that my append statement *deletes* elements of my tuple? The > entire code follows: > There isn't a tuple is sight there - you are dealing with lists, and you are modifying the very list you are iterating over.
Try rewriting the code to create a new list from the old one (i.e. iterate over catChains and have your code append to an initially empty list called, for example, newCatChains, then finally throw the old list away with catChains = newCatChains or some such). [code snipped] > > PS (Mainly, I believe, for Carsten): While programming is difficult for > me, I am writing (and have pretty much finished) this (almost) fully > automated shopping cart. I don't intend to write any other serious > programming project. However, a shopping cart is vital to my Web design > business. I will hereafter outsource my programming. But, as any good > supervisor knows, one has to know how to supervise! If I can't read > code, then I'm at the mercy of my programmer(s). If I can't afford to > hire some top gun who can supervise, then it's my responsibility. Plus, > if my programmer(s) quit, I need to step in and take over. I'm an ok > businessman, and absolutely gifted in sales. And in poetry ;) > beno > Given that there are umpteen thousand hosting services who will let you create a web site with shopping cart included I have to question whether you are making the best use of your time here. Of course it's your time, and your decision, so please don't think I am dictating to you. While the learning you have performed in getting this system to work (for some rather questionable value of "work", I can't help feeling, but we'll overlook the horrors induced by your lack of programming experience) is a testament to your persistence (and this list's tolerance) I can't help feeling that it leaves you no better qualified to supervise programmers. regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 PyCon is coming! Atlanta, Feb 2010 http://us.pycon.org/ Holden Web LLC http://www.holdenweb.com/ UPCOMING EVENTS: http://holdenweb.eventbrite.com/ -- http://mail.python.org/mailman/listinfo/python-list
