This handler extends the functionality of the FileHandler by "rotating" the log file when it reaches a certain size. maxBytes specifies the maximum size in bytes that the log file can grow to before rolling over to a new one. If the size of the new log message plus the current log file size exceeds maxBytes then a roll-over is triggered. When a roll-over occurs, before the log message is written, the log file is renamed and appended with .1. If a .1 version already existed, it would have been renamed .2 first and so on. The maximum number of log files to keep is specified by maxBackupCount. After the renames are complete the log message is written to the original, now blank, file.