On 03/30/2017 04:23 PM, Pavol Lisy wrote:
On 3/30/17, Nick Coghlan <ncoghlan@gmail.com> wrote:
On 30 March 2017 at 19:18, Markus Meskanen <markusmeskanen@gmail.com> wrote:
d = [[0] * 5 for _ in range(10)]
d = [[0]*5]*10 # what about this?
These are not quite the same when the repeated object is mutable. Compare:
matrix1 = [[0] * 5 for _ in range(10)] matrix1[0].append(1) matrix1 [[0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
matrix2=[[0]*5]*10 matrix2[0].append(1) matrix2 [[0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 1]]
so the comprehension is usually necessary. Wolfgang