remove_last_line.py

import os

CHUNK_SIZE = 1024


def remove_last_line(path):
    with open(path, 'rb+') as f:
        def process_chunk(base_offset, chunk):
            try:
                f.seek(base_offset + chunk.rindex(b'\n'), os.SEEK_SET)
            except ValueError:
                return False
            f.truncate()
            return True

        f.seek(0, os.SEEK_END)
        pos = f.tell() - 1
        f.seek(pos, os.SEEK_SET)
        last_char = f.read(1)
        if last_char == b'\n':
            f.seek(pos, os.SEEK_SET)
            f.truncate()

        while True:
            if pos < CHUNK_SIZE:
                f.seek(0, os.SEEK_SET)
                process_chunk(0, f.read(pos))
                break

            pos -= CHUNK_SIZE
            f.seek(pos, os.SEEK_SET)
            if process_chunk(pos, f.read(CHUNK_SIZE)):
                break