### 6.29.5.3 RotatingFileHandler

The `RotatingFileHandler` class supports rotation of disk log files.

class `RotatingFileHandler`( | filename[, mode[, maxBytes[, backupCount]]])

  Returns a new instance of the `RotatingFileHandler` class. The specified file is opened and used as the stream for logging. If mode is not specified, `'a'` is used. By default, the file grows indefinitely.

  You can use the maxBytes and backupCount values to allow the file to rollover at a predetermined size. When the size is about to be exceeded, the file is closed and a new file is silently opened for output. Rollover occurs whenever the current log file is nearly maxBytes in length; if maxBytes is zero, rollover never occurs. If backupCount is non-zero, the system will save old log files by appending the extensions ".1", ".2" etc., to the filename. 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, up to app.log.5. The file being written to is always app.log. When this file is filled, 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.

`doRollover`( | )

  Does a rollover, as described above.

`emit`( | record)

  Outputs the record to the file, catering for rollover as described previously.