Question about nested lists!

[rainlet]

I use a nested list to make a 2-d array. The code follows:

    floor_member = [ 0 ]
                                                                                
    for x in range ( 9 ) :
        floor_member.append ( 0 )
                                                                                
    floor = [ floor_member ]
                                                                                
    for y in range ( 9 ) :
        floor.append ( floor_member )
                                                                                
    floor [ 5 ] [ 5 ] = 1
                                                                                
    for n in range ( 10 ) :
        print floor [ n ]
#code end

I only assign floor [ 5 ] [ 5 ] = 1, but the result is :

[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0]


Is this a bug? Please help me debug. I can't see anything wrong!
Thank you!