How to modify the data in a binary file?
omer at no-log.org
Wed Jul 2 14:15:38 CEST 2008
Le Wednesday 02 July 2008 14:05:39 Jim Brown, vous avez écrit :
> Hi all, I'm a Python newbie, so please pardon me if my question may look a
> little silly. :)
> I want to modify a binary file p.data (which has some C-style "short"
> integers -- 16-bit integers) in such a way:
> The bit m and bit n of every "short int" si in the file are set to 1, and
> the left bits in si are not affected.
> I.e, for the first short int in the file, I think the code would be:
> import os
> f = os.open("/root/p.data", os.O_RDWR)
> str = os.read(f, 2)
> #assume the short int in str is 0x0102, and I want to change it to 0x8182
> (changing bit7 and bit15 to 1).
> #how to change the str into a short int variable si??
> si = (si & ~0x8080) | 0x8080
You can either do it by hand by splitting your string in chars and getting the
bytes values with ord (described here:
byte0 = ord(s)
byte1 = ord(s)
si = (byte0 << 8) | byte1 # or maybe the inverse ?
or use the struct module:
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