String replacing in a file by given position

Question

I have a file opened in 'ab+' mode.

What I need to do is replacing some bytes in the file with another string's bytes such that:

FILE:

thisissomethingasperfectlygood.

string:

01234

So, for example, I seek for the position (4, 0) and I want to write 01234 in the place of "issom" in the file. Last appearance would be:

this01234ethingasperfectlygood.

There are some solutions on the net, but all of them (at least what I could find) are based on "first find a string in the file and then replace it with another one". Because my case is based on seeking, so I am confused about the solution.

Answer 1

You could mmap() your file and then use slice notation to update specific byte ranges in the file. The example here should help.

Answer 2

You can use mmap for that

import os,mmap
f=os.open("afile",os.O_RDWR)
m=mmap.mmap(f,0)
m[4:9]="01234"
os.close(f)