class RotatingFileHandler(BaseRotatingHandler):
    """
    Handler for logging to a set of files, which switches from one file
    to the next when the current file reaches a certain size.
    """

    FS = "%s" + os.linesep

    def __init__(self, filename, mode='a', maxBytes=0, backupCount=0,
                 encoding=None, delay=0):
        """
        Open the specified file and use it as the stream for logging.

        By default, the file grows indefinitely. You can specify particular
        values of maxBytes and backupCount to allow the file to rollover at
        a predetermined size.

        Rollover occurs whenever the current log file is nearly maxBytes in
        length. If backupCount is >= 1, the system will successively create
        new files with the same pathname as the base file, but with extensions
        ".1", ".2" etc. appended to it. For example, with a backupCount of 5
        and a base file name of "app.log", you would get "app.log",
        "app.log.1", "app.log.2", ... through to "app.log.5". The file being
        written to is always "app.log" - when it gets filled up, it is closed
        and renamed to "app.log.1", and if files "app.log.1", "app.log.2" etc.
        exist, then they are renamed to "app.log.2", "app.log.3" etc.
        respectively.

        If maxBytes is zero, rollover never occurs.
        """
        # If rotation/rollover is wanted, it doesn't make sense to use another
        # mode. If for example 'w' were specified, then if there were multiple
        # runs of the calling application, the logs from previous runs would
        # be lost if the 'w' is respected, because the log file would be
        # truncated on each run.
        if maxBytes > 0:
            mode = 'a'
        BaseRotatingHandler.__init__(self, filename, mode, encoding, delay)
        self.maxBytes = maxBytes
        self.backupCount = backupCount

    def doRollover(self):
        """
        Do a rollover, as described in __init__().
        """
        if self.stream:
            self.stream.close()
            self.stream = None
        if self.backupCount > 0:
            for i in range(self.backupCount - 1, 0, -1):
                sfn = "%s.%d" % (self.baseFilename, i)
                dfn = "%s.%d" % (self.baseFilename, i + 1)
                if os.path.exists(sfn):
                    if os.path.exists(dfn):
                        os.remove(dfn)
                    os.rename(sfn, dfn)
            dfn = self.baseFilename + ".1"
            if os.path.exists(dfn):
                os.remove(dfn)
            os.rename(self.baseFilename, dfn)
        self.mode = 'w'
        self.stream = self._open()

    def shouldRollover(self, record):
        """
        Determine if rollover should occur.

        Basically, see if the supplied record would cause the file to exceed
        the size limit we have.
        """
        if self.stream is None:
            # delay was set...
            self.stream = self._open()
        if self.maxBytes > 0:
            # are we rolling over?
            length = self.entryLength(self, record)
            self.stream.seek(0, 2)
            #due to non-posix-compliant Windows
            if self.stream.tell() + length >= self.maxBytes:
                return 1
        return 0

    def entryLength(self, record):
        """
        Determine entry length in bytes.
        """
        msg = self.format(record)
        if (logging._unicode and isinstance(msg, unicode) and
                getattr(self.stream, 'encoding', None)):
            encoding = self.stream.encoding
            entry = self.FS.decode(encoding) % msg
            return len(entry.encode(encoding))

        return len(self.FS % msg)