swapping numeric items in a list

[Jiang Nutao]

Hi,

I simplify my problem like below

To convert list
    aa = [0x12, 0x34, 0x56, 0x78]
into
    [0x34, 0x12, 0x78, 0x56]

How to do it fast? My real list is huge.

Thanks a lot.
Jason