logging in python
logging in python
Logging provides a set of convenience functions for simple logging usage.
These are debug(), info(), warning(), error() and critical(). To determine when to use logging, see the table below, which states, for each of a set of common tasks, the best tool to use for it. The standard levels and their applicability are described below (in increasing order of severity):
| Level | When it’s used |
|---|---|
| DEBUG | Detailed information, typically of interest only when diagnosing problems. |
| INFO | Confirmation that things are working as expected. |
| WARNING | An indication that something unexpected happened, or indicative of some problem in the near future (e.g. ‘disk space low’). The software is still working as expected. |
| ERROR | Due to a more serious problem, the software has not been able to perform some function. |
| CRITICAL | A serious error, indicating that the program itself may be unable to continue running. |
class logging.handlers.RotatingFileHandler
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. If encoding is not None, it is used to open the file with that encoding.
If delay is true, then file opening is deferred until the first call to emit(). 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 either of maxBytes or backupCount 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.
- Example
import logging
import logging.config
logging.config.fileConfig('logging.conf')
# create logger
logger = logging.getLogger('simpleExample')
# 'application' code
logger.debug('debug message')
logger.info('info message')
logger.warn('warn message')
logger.error('error message')
logger.critical('critical message')
#Here is the logging.conf file:
[loggers]
keys=root,simpleExample
[handlers]
keys=consoleHandler
[formatters]
keys=simpleFormatter
[logger_root]
level=DEBUG
handlers=consoleHandler
[logger_simpleExample]
level=DEBUG
handlers=consoleHandler
qualname=simpleExample
propagate=0
[handler_consoleHandler]
class=logging.handlers.RotatingFileHandler
level=DEBUG
formatter=simpleFormatter
args=('/var/log/simpleExample.log', 'a', 10*1024*1024, 1)
[formatter_simpleFormatter]
format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
datefmt=