将元组插入2D数组

Question

我试图将一些元组插入到2D数组中，但由于某种原因，x值似乎没有增加。

x_axis = 20
y_axis = 4
arr = [[None]*y_axis]*x_axis
for x in range(x_axis):
    for y in range(y_axis):
        arr[x][y] = (x,9,y,6)

for x in range(x_axis):
    for y in range(y_axis):
        print arr[x][y]

我得到了这个：

(19, 9, 0, 6)
(19, 9, 1, 6)
(19, 9, 2, 6)
(19, 9, 3, 6)
(19, 9, 0, 6)
(19, 9, 1, 6)
(19, 9, 2, 6)
(19, 9, 3, 6)
(19, 9, 0, 6)
(19, 9, 1, 6)
(19, 9, 2, 6)
(19, 9, 3, 6)
(19, 9, 0, 6)
(19, 9, 1, 6)
(19, 9, 2, 6)
(19, 9, 3, 6)
(19, 9, 0, 6)
(19, 9, 1, 6)
(19, 9, 2, 6)
(19, 9, 3, 6)

我不知道x为什么坚持19（范围的最后一个数字）而不仅仅是0-19（包括0-19）。