Fast tail(1) implementation using mmap in Python

fast_tail_using_mmap.py

import os
import sys
import mmap


def tail(filepath, numlines):
    with open(filepath, 'rb') as f:
        mapped = mmap.mmap(f.fileno(), 0, mmap.MAP_SHARED, mmap.PROT_READ)
        size = os.stat(filepath).st_size
        try:
            for i in range(size - 1, -1, -1):
                if mapped[i] == '\n':
                    numlines -= 1
                    if numlines < 0:
                        break
            return mapped[i + 1 if i > 0 else 0:]
        finally:
            mapped.close()


def main():
    if len(sys.argv) != 3:
        sys.stderr.write('Usage: {0} /path/to/file N\n'.format(sys.argv[0]))
        return 1

    sys.stdout.write(''.join(tail(sys.argv[1], int(sys.argv[2]))))
    return 0


if __name__ == '__main__':
    sys.exit(main())