Python - Parse file into outputs based on magic number/length

I'm a complete beginner to coding - only started 3 weeks ago, and really only have codecademy's Python course under my belt - so simple explanations would be really appreciated!

I'm trying to write a python script that reads a file as a HEX string, and then parses the file into individual output files based on finding a "magic number" within the HEX string.

EG: if my HEX string were "0011AABB00BBAACC00223344", I might want to parse this string into new output files based on the magic number "00", and telling python that each output should be 8 characters long. The output for the example string above should be 3 files that contain the HEX values:

"0011AABB" "00BBAACC" "00223344"

Here's what I have so far (assuming in this case that the string above is contained within the "hextests" file

import os
import binascii

filename = "hextests"

# read file as a binary string
with open(filename, 'rb') as f:
    content = f.read()

# convert binary string to hex string
hexString = binascii.hexlify(content)

# define magic number as "00"
magic_N = "00"

# attempting to create a new substring called newFile that is equal to each instance magic_N repeats throughout the file for a length of 8 characters
for chars in hexString:
    newFile = ""
    if chars == magic_N:
        newFile += chars.len(9)

# attempting to create a series of new output files for each instance of newFile - while incrementing the output file name
    if newFile != "":
        i = 0
        while os.path.exists("output_file%s.xyz" % i):
          i += 1
        fh = with open("output_file%s.xyz" % i, "wb"):
            newFile

I'm sure I have a lot of errors to work through on this - and it's likely more complicated than I think .... but my main question has to do with the proper way to define the chars and newFile variables. I'm pretty sure python sees chars as only single characters in the string, so it's failing because I'm attempting to search for a magic_N that is longer than 1 character. Am I correct that that is part of the issue?

Also, if you understand the main goal of this script, any other thoughts about things I should be doing differently?

Thanks so much for the help!