Thanks for the info. I did not know that. Thanks Vincent Davis
On Sat, Jan 24, 2009 at 10:46 AM, Steve Holden <st...@holdenweb.com> wrote: > Vincent Davis wrote: > > I have a short peace of code that is not doing what I expect. when I > > assign a value to a list in a list alist[2][4]=z this seems replace all > > the 4 elements in all the sub lists. I assume it is supposed to but this > > is not what I expect. How would I assign a value to the 4th element in > > the 2nd sublist. here is the code I have. All the printed values are > > what I would expect except that all sublist values are replaced. > > > > Thanks for your help > > Vincent > > > > on the first iteration I get ; > > new_list [[None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None], > > [None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None]] > > > > and expected this; > > new_list [[None, 0, 1, None], [None, None, None, None], > > [None, None, None, None], [None, None, None, None], [None, None, None, > > None], [None, None, None, None]] > > > > Code; > > list1=[[1,2],[0,3,2,1],[0,1,3],[2,0,1],[3],[2,3]] > > new_list=[[None]*4]*6 > > print 'new_list',new_list > > for sublist in range(6): # 6 becuase it is the # of rows lists1 > > print 'sublist', sublist > > for x in list1[sublist]: > > print list1[sublist] > > print 'new_list[sublist][x]', new_list[sublist][x] > > new_list[sublist][x]=list1[sublist].index(x) > > print 'sublist', sublist, 'x', x > > print new_list[sublist][x] > > print 'new_list', new_list > > > When you create new_list you are actually filling it with six references > to the same list. Consequently when you change one of those list > elements they all appear to change (because they are all referencing the > same list object). > > Try instead > > new_list = [[None]*4 for i in range(6)] > > and you should find your code works as expected. In this case the list > is constructed with a new sublist as each element. > > regards > Steve > -- > Steve Holden +1 571 484 6266 +1 800 494 3119 > Holden Web LLC http://www.holdenweb.com/ > > -- > http://mail.python.org/mailman/listinfo/python-list >
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