Question

THIS SHOULD BE EASY! But i’ve been unable to find the answer to this question.

Using python, I want to read a binary file into memory, modify the first four bytes of the file, and then write the file back.

There has to be a simple way to edit four measly bytes! right?

Answer 1

Why read the entire file to change four bytes at the beginning? Shouldn’t this work?

with open("filename.txt", "r+b") as f:
     f.write(chr(10) + chr(20) + chr(30) + chr(40))

Even if you need to read these bytes from the file to calculate the new values, you could still do:

with open("filename.txt", "r+b") as f:
    fourbytes = [ord(b) for b in f.read(4)]
    fourbytes[0] = fourbytes[1]  # whatever, manipulate your bytes here
    f.seek(0)
    f.write("".join(chr(b) for b in fourbytes))