Split file by specific string

split_file.py

import mmap
import os
from sys import stdout
from sys import exit

#  If length is 0, the maximum length of the map is the current size of the file
FIND_BUFFER_SIZE = 0
READ_BUFFER_SIZE = 100
SEARCH_STRING = "substring3.1"

f = open('example.txt')
mmf = mmap.mmap(f.fileno(), FIND_BUFFER_SIZE, access=mmap.ACCESS_READ)

index = mmf.find(SEARCH_STRING)

if index == -1:
    print("string not found")
    exit(-1)

mmf.seek(index, os.SEEK_SET)

length = mmf.size()
while True:
    stdout.write(mmf.read(READ_BUFFER_SIZE))
    if length == mmf.tell():
        break