Add Hex characters in a file with python

Question

I would like to add a list of specific Hex characters at the first line of my file.

bin = "420d0d0a010000000000000000000000"

file1:

e300 0000 0000 0000 0000 0000 0002 0000
0040 0000 0073 6a00 0000 6400 6401 6c00
5a00 6400 6401 6c01 5a01 6400 6401 6c02
5a02 6400 6401 6c03 5a03 6400 6401 6c02
...

file2:

420d 0d0a 0100 0000 0000 0000 0000 0000
e300 0000 0000 0000 0000 0000 0002 0000
0040 0000 0073 6a00 0000 6400 6401 6c00
5a00 6400 6401 6c01 5a01 6400 6401 6c02
5a02 6400 6401 6c03 5a03 6400 6401 6c02
...

I would like to get the file2.

I tried that:

bin = "420d0d0a010000000000000000000000"

def change_hex():
    with open("file.txt") as f: 
        lines = f.readlines()

    lines[0] = f"{bin}\n"

    with open("file.txt", "w") as f:
        f.writelines(lines)

But it didn't work, I had this error:

UnicodeDecodeError: 'charmap' codec can't decode byte 0x8f in position 174: character maps to <undefined>

Maybe it's not the right thing to do?

Thanks in advance, have a good day.

But precisely, I don't know why it didn't work, that's also why I'm asking for help. — Tibo1211
– Tibo1211, Commented Feb 5, 2021 at 2:51
Is this a hexdump or the actual file content? Also, please include the full traceback of the error. — SuperStormer
– SuperStormer, Commented Feb 5, 2021 at 2:55
you probably need to open the file as binary, but it's difficult to know exactly what's wrong — Pedro Lobito
– Pedro Lobito, Commented Feb 5, 2021 at 3:02

SuperStormer · Accepted Answer · 2021-02-05 03:12:08Z

1

You need to open your files in binary mode and to convert the hex str to bytes using bytes.fromhex.

header = bytes.fromhex("420d0d0a010000000000000000000000")

def change_hex():
    with open("file.txt", "rb") as f: 
        content = f.read()

    with open("file.txt", "wb") as f:
        f.write(header)
        f.write(content)

answered Feb 5, 2021 at 3:12

SuperStormer

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1 Comment

Tibo1211 Over a year ago

WOW, IT WORKS, thank you very much, thank you for taking the time to help me. Have a good day ! <3

leandroian · Accepted Answer · 2021-02-05 02:54:10Z

0

The problem is you are replacing the first line for your new line, but you need to append the new line to the beginning.

Just try replacing this line

lines[0] = f"{bin}\n"

For this

lines.insert(0,bin)

answered Feb 5, 2021 at 2:54

leandroian

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1 Comment

Tibo1211 Over a year ago

Hi, thanks for your answer, but I got the same error:

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