swapping numeric items in a list

[Fredrik Lundh]

Jiang Nutao wrote:

> array.byteswap() won't work for me easily. I tried this before my 1st post. 
> I defined
> 
>     aa = array('H', [0x12, 0x34, 0x56, 0x78])
> 
> Then did byteswap aa.byteswap(). The result was
> 
>     array('H', [0x1200, 0x3400, 0x5600, 0x7800])
> 
> You can see it byteswapped within each item.

you need to do things in the right order; first convert to bytes, then 
build a 16-bit array, and then byteswap that array.

from array import array

# convert data array to 8-bit byte buffer
buf = array("B", [0x12, 0x34, 0x56, 0x78]).tostring()

# treat byte buffer as list of 16-bit integers
buf = array("H", buf)
buf.byteswap()

buf = buf.tostring() # convert back to bytes

[hex(ord(c)) for c in buf]
-> ['0x34', '0x12', '0x78', '0x56']

</F>