Read last line of a file

tail.py

def read_last_line(fd):
    """ 
    Efficiently read the last line of a file by seeking to the
    end of the file and looping backwards until the first linefeed
    character is encountered. Ignores trailing newlines at the EOF
    """
    # seek to the end of the file
    fd.seek(0, 2)
    size = fd.tell()
    if size == 0:
        return ''
    BLOCKSIZE = min(size, 512)  # bytes
    pos = 0 
    while pos + BLOCKSIZE <= size:
        # seek to next block
        pos += BLOCKSIZE
        fd.seek(-pos, 1)
        s = fd.read()
        try:
            if s.index('\n') != len(s) - 1:
                return '\n'.join(s.rsplit('\n', 2 if s.endswith('\n') else 1)[1:])
        except ValueError:
            continue
    return s