Python list of lists
I just stumbled upon a post/problem in stackoverflow. Here I discuss it and the solution. First check the following code segment : >>>visited = [[False]*4]*4 >>>visited[0][1] = True >>>print visited >>> [[False, True, False, False], [False, True, False, False], [False, True, False, False], [False, True, False, False]] Do you see the problem, second element of all the list changed to True! So it means [[False]*4]*4 creates a list that contains reference to the same list [False, False, False, False] You can avoid this by following this code: >>> n = 4 >>> m = 4 >>> visited = [] >>> for x in xrange(n): ... visited.append([False] * m) ... >>> visited [[False, False, False, False], [False, False, False, False], [False, False, False, False], [False, False, False, False]] >>> visited[0][1] = True >>> visited [[False, True, False, False],...