## {{{ http://code.activestate.com/recipes/439045/ (r2)
#!/usr/bin/env python
# -*-mode: python; coding: iso-8859-1 -*-
#
# Copyright (c) Peter Astrand <astrand@cendio.se>
# $Id$
# $URL$

import string

class BackwardsReader:
    """Read a file line by line, backwards"""

    def readline(self):
        while 1:
            newline_pos = string.rfind(self.buf, "\n")
            pos = self.file.tell()
            if newline_pos != -1:
                # Found a newline
                line = self.buf[newline_pos+1:]
                self.buf = self.buf[:newline_pos]
                if pos != 0 or newline_pos != 0 or self.trailing_newline:
                    line += "\n"
                return line
            else:
                if pos == 0:
                    # Start-of-file
                    return ""
                else:
                    # Need to fill buffer
                    toread = min(self.BLKSIZE, pos)
                    self.file.seek(-toread, 1)
                    self.buf = self.file.read(toread) + self.buf
                    self.file.seek(-toread, 1)
                    if pos - toread == 0:
                        self.buf = "\n" + self.buf

    def __init__(self, file, BLKSIZE=4096):
        self.file = file
        self.BLKSIZE = BLKSIZE
        self.buf = ""
        self.file.seek(-1, 2)
        self.trailing_newline = 0
        lastchar = self.file.read(1)
        if lastchar == "\n":
            self.trailing_newline = 1
            self.file.seek(-1, 2)