#!/usr/bin/env python3

import io

def reverse_lines(*args, **kwargs):
    with open(*args, **kwargs) as f:
        buf = ''
        f.seek(0, io.SEEK_END)
        while f.tell():
            try:
                f.seek(-1024, io.SEEK_CUR)
            except OSError:
                bufsize = f.tell()
                f.seek(0, io.SEEK_SET)
                newbuf = f.read(bufsize)
                f.seek(0, io.SEEK_SET)
            else:
                newbuf = f.read(1024)
                f.seek(-1024, io.SEEK_CUR)
            buf = newbuf + buf
            lines = buf.split('\n')
            buf = lines.pop(0)
            yield from reversed(lines)
        yield buf

def test_reversed():
    with open('bigfile.txt') as f:
        for _ in reversed(list(f)):
            pass

def test_revlines():
    list(reverse_lines('bigfile.txt'))

def makefile(count):
    import random
    import string
    with open('bigfile.txt', 'w') as f:
        for _ in range(count):
            f.write(''.join(random.choice(string.ascii_letters)
                            for _ in range(72)) + '\n')

if __name__ == '__main__':
    import timeit
    for count in 100, 1000, 10000, 100000, 1000000:
        makefile(count)
        treversed = timeit.timeit(test_reversed, number=1000000//count)
        trevlines = timeit.timeit(test_revlines, number=1000000//count)
        print('{:8} lines: {} reversed, {} revlines'.format(
            count, treversed, trevlines))