I'm programming with lists and have run into a problem. width = 2 height = 2 # Traverse the board def traverse(x, y): # The four possible directions squares = [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)] print squares # Remove impossible squares for square in squares: print "now accessing", square if (square[0] < 1 or square[0] > width or square[1] < 1 or square[1] > height or square == (1, height)): squares.remove(square) print "removed", square print(squares) # Testing traverse traverse(1,1) This results in the following output: [(0, 1), (2, 1), (1, 0), (1, 2)] now accessing (0, 1) removed (0, 1) now accessing (1, 0) removed (1, 0) [(2, 1), (1, 2)] It completely skips the elements (2,1) and (1,2) -- without even checking them! I found answers here saying I shouldn't be modifying a list while traversing it, and that definitely makes sense. But can someone tell me why it doesn't work? What's behind the veil of Python lists? Continue reading...
