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How do RotatingFileHandler and TimedRotatingFileHandler prevent log files from growing unbounded?

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Answer

RotatingFileHandler rotates the log file once it reaches a specified maxBytes, renaming old files with numeric suffixes and keeping up to backupCount old files. TimedRotatingFileHandler instead rotates on a time interval (e.g., daily, hourly). Both prevent a single log file from consuming unlimited disk space over a long-running application's lifetime.
from logging.handlers import RotatingFileHandler

handler = RotatingFileHandler('app.log', maxBytes=10_000_000, backupCount=5)
logger = logging.getLogger('myapp')
logger.addHandler(handler)
Real-world example A long-running background worker uses TimedRotatingFileHandler(when='midnight', backupCount=30) to keep exactly 30 days of daily log files and auto-delete older ones.

Common follow-ups: What happens to the currently-open file handle during rotation?;How does this differ from external log rotation tools like logrotate?

File I/O & Context Managers;Memory Management & Garbage Collection
All 15 Logging questions