On Tue, Nov 3, 2009 at 4:20 PM, Robert Berman <berma...@cfl.rr.com> wrote:
> > In [69]: l1=[(0,0)] * 4 > > In [70]: l1 > Out[70]: [(0, 0), (0, 0), (0, 0), (0, 0)] > > In [71]: l1[2][0] > Out[71]: 0 > > In [72]: l1[2][0] = 3 > --------------------------------------------------------------------------- > TypeError Traceback (most recent call last) > > /home/bermanrl/<ipython console> in <module>() > > TypeError: 'tuple' object does not support item assignment > > First question, is the error referring to the assignment (3) or the index > [2][0]. I think it is the index but if that is the case why does l1[2][0] > produce the value assigned to that location and not the same error message. > > Second question, I do know that l1[2] = 3,1 will work. Does this mean I > must know the value of both items in l1[2] before I change either value. I > guess the correct question is how do I change or set the value of l1[0][1] > when I specifically mean the second item of an element of a 2D array? > > I have read numerous explanations of this problem thanks to Google; but no > real explanation of setting of one element of the pair without setting the > second element of the pair as well. > > For whatever glimmers of clarity anyone can offer. I thank you. > Tuples are immutable types. Thus it is not possible to change one of the values of a tuple (or even of changing both of them). The only thing you can do, is create a new tuple, and put that in the same place in the list. In your example, when you do l1[2][0] = 3, you try to change the tuple l1[2], which is impossible. To do what you want to do, you have to create a new array with the same second but different first value, and put that array in l1[2], that is: l1[2] = (3, l1[2,1]) -- André Engels, andreeng...@gmail.com
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