Python - decode('hex')

[MRAB]

On 2017-02-20 17:55, Ganesh Pal wrote:
> Hello Python world,
>
> I  am on Linux and Python 2.7 ,  I need some help to figure out what is
> going  wrong in the below piece of code
>
> I am trying to replace seven bytes in the hexdumfile at a given offset
>
>
> Program 1 works fine
>
> #!/usr/bin/python
> from qa.utils.easy_popen import run
> import pdb
>
> def replace_hex(fname, offset, newdata):
>     #pdb.set_trace()
>     with open(fname, 'r+b') as f:
>         #Show current contents
>         f.seek(offset)
>         stringdata = f.read(len(newdata))
>         print 'Current data:'
>         print '%08X: %s\n' % (offset, stringdata.encode('hex'))
>
>         #Replace data at offset with newdata
>         f.seek(offset)
>         f.write(newdata)

There's no need to explicitly close the file because when you leave the 
'with' statement, it'll close the file for you; that's why it's used!

>         f.close()

It's best to unindent the following lines so that they're outside the 
'with' statement (and the file will have been closed).

>         #print the data
>         cmd = 'hexdump -C %s' % (fname)
>         print cmd
>         out, err, ret = run(cmd)
>         print "Hexdump file data for corrupting"
>         print out, err, ret
>         return fname
>
> fname = '/tmp/2017-02-20_08-42-22/file1.raw'
> offset = 0x1
> newdata = '64000101057804'.decode('hex')
>
> replace_hex(fname, offset, newdata)
>
>
> -200-1# python file_2.py
> Current data:
> 00000001: 6400010105789a
>
> hexdump -C /tmp/2017-02-20_08-42-22/file1.raw
> Hexdump file data for corrupting
> 00000000  06 64 00 01 01 05 78 04  73 1c ab 58 08 f9 8b 3b
>  |.d....x.s..X...;|  ==> Replaced
> 00000010  1e 00 a1 00 01 00 00 00  64 00 01 01 05 78 02 00
>  |........d....x..|
>
[snip]