for a[x] in a: print(a) Except for when x = 0, a[x] never takes on its original value throughout the iterations
So for x = 0, we get: [0, 1, 2, 3] [1, 1, 2, 3] [2, 1, 2, 3] [3, 1, 2, 3] For x = 1: [0, 0, 2, 3] [0, 0, 2, 3] [0, 2, 2, 3] [0, 3, 2, 3] For x = 2: [0, 1, 0, 3] [0, 1, 1, 3] [0, 1, 1, 3] [0, 1, 3, 3] How is the array being transformed? On 29 June 2017 at 14:32, Alan Gauld via Tutor <tutor@python.org> wrote: > On 29/06/17 03:14, shubham goyal wrote: > > > This Question is asked in some exam. i am not able to figure it out. > > > > a = [0, 1, 2, 3] > > for a[-1] in a: > > print(a[-1]) > > > > its giving output 0 1 2 2 > > > > it should be 3 3 3 3 as a[-1] belongs to 3. > > can anyone help me figuring it out. > > This is quite subtle and it took me a few minutes to figure > it out myself. > > It might be clearer if we print all of 'a' instead > of a[-1]: > > >>> for a[-1] in a: > ... print(a) > ... > [0, 1, 2, 0] > [0, 1, 2, 1] > [0, 1, 2, 2] > [0, 1, 2, 2] > > What is happening is that a[-1] is being assigned the value > of each item in a in turn. The final iteration assigns a[-1] > to itself, thus we repeat the 2. > > Another way to see it is to convert the for loop to > a while loop: > > for variable in collection: > process(variable) > > becomes > > collection = [some sequence] > index = 0 > while index < len(collection): > variable = collection[index] > process(variable) > index += 1 > > Now substitute your values: > > collection = [0,1,2,3] > index = 0 > while index < len(collection): > collection[-1] = collection[index] > print(collection[-1]) > index += 1 > > Does that help? > > -- > Alan G > Author of the Learn to Program web site > http://www.alan-g.me.uk/ > http://www.amazon.com/author/alan_gauld > Follow my photo-blog on Flickr at: > http://www.flickr.com/photos/alangauldphotos > > > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor > -- Thank you Anupama _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
