What is the point of setLevel in a python logging handler?

by

It allows finer control. By default the root logger has WARNING level set, this means that it wont print messages with lower level(no matter how the handlers’ levels are set!). But, if you set the root logger’s level to DEBUG, indeed the message get sent to the log file:

import logging
import logging.handlers

a = logging.getLogger('myapp')
a.setLevel(logging.DEBUG)   # set root's level
h = logging.handlers.RotatingFileHandler('foo.log')
h.setLevel(logging.DEBUG)
a.addHandler(h)
print a.getEffectiveLevel() 
a.debug('foo message')
a.warn('warning message')

Now, image that you want to add a new handler that doesn’t record debug information.
You can do this by simply setting the handler logging level:

import logging
import logging.handlers

a = logging.getLogger('myapp')
a.setLevel(logging.DEBUG)   # set root's level

h = logging.handlers.RotatingFileHandler('foo.log')
h.setLevel(logging.DEBUG)
a.addHandler(h)

h2 = logging.handlers.RotatingFileHandler('foo2.log')
h2.setLevel(logging.WARNING)
a.addHandler(h2)

print a.getEffectiveLevel() 
a.debug('foo message')
a.warn('warning message')

Now, the log file foo.log will contain both messages, while the file foo2.log will only contain the warning message. You could be interested in having a log file of only error-level messages, then simply add a Handler and set its level to logging.ERROR, everything using the same Logger.

You may think of the Logger logging level as a global restriction on which messages are “interesting” for a given logger and its handlers. The messages that are considered by the logger afterwards get sent to the handlers, which perform their own filtering and logging process.

More Related Contents:

  1. String formatting: % vs. .format vs. f-string literal
  2. Where is a complete example of logging.config.dictConfig?
  3. How to disable logging on the standard error stream?
  4. Read from a log file as it’s being written using python
  5. TypeError: only length-1 arrays can be converted to Python scalars while trying to exponentially fit data
  6. Logging, StreamHandler and standard streams
  7. How to add a custom loglevel to Python’s logging facility
  8. Logging to two files with different settings
  9. using Python logger class to generate multiple logs for different log levels
  10. How to easily print ascii-art text? [closed]
  11. Logging within pytest tests
  12. Get Output From the logging Module in IPython Notebook
  13. logging with filters
  14. real time subprocess.Popen via stdout and PIPE
  15. How can I disable logging while running unit tests in Python Django?
  16. Log exception with traceback in Python
  17. Lazy logger message string evaluation
  18. How do I log from my Python Spark script
  19. Suppress newline in Python logging module
  20. Naming Python loggers
  21. Python logging: use milliseconds in time format
  22. Django Setup Default Logging
  23. How to use logging.getLogger(__name__) in multiple modules
  24. Run subprocess and print output to logging
  25. Does python logging flush every log?
  26. How to log Keras loss output to a file
  27. redirect prints to log file
  28. Python – How to check if a file is used by another application?
  29. Python Logging – Disable logging from imported modules
  30. Redirect Python ‘print’ output to Logger

Leave a Comment