logginghandlers

Logging handlers are components of the Python standard library's logging package that determine where log records are delivered. The logging.handlers module extends the basic set of handlers with additional destinations and behaviors, enabling more sophisticated logging setups without changing the core logging interface.

Each handler is attached to a logger and can have its own level, formatter, and filters. When a logger emits a record, it is passed to each attached handler, and the handlers decide whether to emit the record based on their level and filters. The logging.handlers module provides a variety of built-in handlers for files, network destinations, and other targets.

RotatingFileHandler and TimedRotatingFileHandler manage log file rotation. RotatingFileHandler rotates when a file reaches a size threshold and keeps a number of backup files. TimedRotatingFileHandler rotates at regular time intervals (e.g., hourly or daily), also maintaining backups. These help prevent unbounded log growth.

Network and system destinations include SocketHandler and DatagramHandler for sending records to a remote server over TCP or UDP; SysLogHandler for syslog; and SMTPHandler for email alerts. MemoryHandler buffers records in memory and flushes them to a target handler, which is useful for batching. NullHandler discards records, and QueueHandler with QueueListener enables asynchronous logging to avoid blocking the main application.

Configuration is typically done by code, but can also be established with configuration files or dictionaries via logging.config. A logger can have multiple handlers, allowing simultaneous local file logging, network delivery, or alerting; each handler can use its own formatter to control the appearance of log messages. Because handlers vary in reliability and performance, applications often choose a mix that matches their requirements.

Related concepts include formatters, filters, and the logging configuration system. The logging.handlers module complements the standard Handler base class and is part of the Python standard library used for robust and scalable logging setups.