def revreadlines(self):
        """Fetches a next line backward.

        This is used to locate the trailers at the end of a file.
        """
        self.fp.seek(0, 2)
        pos = self.fp.tell()
        buf = b''
        while 0 < pos:
            prevpos = pos
            pos = max(0, pos-self.BUFSIZ)
            self.fp.seek(pos)
            s = self.fp.read(prevpos-pos)
            if not s:
                break
            while 1:
                n = max(s.rfind(b'\r'), s.rfind(b'\n'))
                if n == -1:
                    buf = s + buf
                    break
                yield s[n:]+buf
                s = s[:n]
                buf = b''
        return
Fetches a next line backward.

        This is used to locate the trailers at the end of a file.