On Sunday 19 August 2007, Pablo Torres wrote: > Hi guys! > > I am working on Conway's Game of Life right now and I've run into a > little problem. > > I represent dead cells with 0s and live ones with 1s. Check this out: > >>> grid = [[0] * 3] * 3 > >>> grid > > [[0, 0, 0], [0, 0, 0], [0, 0, 0]] > > >>> grid[0][0] = 1 > > [[1, 0, 0], [1, 0, 0], [1, 0, 0]] > > Now, that's not what I want. I just want the first element of the > first sublist to be a 1, not the first of every one. Here's what I > tried and didn't work: > > 0. grid = [[0] * 3][:] * 3 then the same grid[0][0] = 1 statement > 1. grid = [[0][:] * 3] * 3 followed by the same assignment > 2. (grid[0])[0] = 1 with the original initialization of the grid > > So, that means that it isn't a problem with two different variables > refering to the same list (0. and 1. prove that). What I don't > understand is why 2. doesn't work either. I'm baby-feeding my > instructions to Python and the mistake is still there. Any ideas?
If you want three copies of the list, you need to copy it thrice (well, twice)
Thus:
>>> row = [0] * 3
>>> grid = []
>>> for n in xrange(3): grid.append(row[:])
...
>>> grid
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> grid[0][0] =1
>>> grid
[[1, 0, 0], [0, 0, 0], [0, 0, 0]]
>>>
--
Regards, Thomas Jollans
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