chunk.py

#!/usr/bin/env python3
# encoding: utf-8
import os
import sys
import argparse


def parse_arguments():
    parser = argparse.ArgumentParser()
    parser.add_argument('file')
    parser.add_argument('-l', '--lines', type=int, default=10,
        help='Specify number of lines to fetch. Default: 10.')

    args = parser.parse_args()
    return args


def main():

    args = parse_arguments()
    # Use 256 bytes as the "base" for one line
    chunk_size = 256*args.lines

    with open(args.file, 'r') as f:
        f.seek(0, os.SEEK_END)
        size = f.tell()

        lines = []
        data = ''
        while len(lines) < args.lines:
            pos = f.tell()-chunk_size
            if pos < 0:
                f.seek(0)
                data = f.read(chunk_size - pos)+data
                lines = data.split('\n') + lines
                break
            f.seek(pos)
            data = f.read(chunk_size)+data
            if '\n' in data:
                s = data.split('\n')
                lines = s[1:] + lines
                data = s[0]

    for line in lines[-args.lines:]:
        print(line, end='\n')

if __name__ == '__main__':
    main()