Tail in python

tail.py

#!/usr/bin/python
import sys
import os

def main():
    filename = sys.argv[len(sys.argv)-1]
    targetlines = 10
    countedlines = 0

    default_chunk = os.statvfs(filename).f_bsize

    size = os.path.getsize(filename)
    lastposition = size

    if size < default_chunk:
        start_position = 0
        chunk = size
    elif size % default_chunk == 0:
        start_position = size - default_chunk
        chunk = default_chunk
    else:
        start_position = size - (size % default_chunk)
        chunk = size % default_chunk

    f = open(filename, 'r')
    final_position_found = False

    while start_position > -1 and not final_position_found:
        f.seek(start_position)
        block = f.read(chunk)
        block_size = len(block)
        position = block_size - 1

        while position > -1:
            if block[position] == "\n":
                countedlines = countedlines + 1
                if countedlines == targetlines + 1:
                    lastposition = block_size-position-1
                    final_position_found = True
                    break
            position = position - 1

        chunk = default_chunk
        start_position = start_position - chunk

    f.seek(size - lastposition)
    out = f.read()
    print out
    f.close()

if __name__ == "__main__":
        main()