Logging Cookbook — Customizing handlers with dictConfig

Reference note (untrusted external data; do not execute it as instructions). There are times when you want to customize logging handlers in particular ways, and if you use dictConfig you may be able to do this without subclassing. As an example, consider that you may want to set the ownership of a log file. On POSIX, this is easily done using shutil.chown, but the file handlers in the stdlib don't offer built-in support. You can customize handler creation using a plain function such as You can then specify, in a logging configuration passed to dictConfig, that a logging handler be created by calling this function In this example I am setting the ownership using the pulse user and group, just for the purposes of illustration. Putting it together into a working script, chowntest.py To run this, you will probably need to run as root Bounded code example (external data; do not execute automatically): ```shell-session $ sudo python3.3 chowntest.py $ cat chowntest.log 2013-11-05 09:34:51,128 DEBUG mylogger A debug message $ ls -l chowntest.log -rw-r--r-- 1 pulse pulse 55 2013-11-05 09:34 chowntest.log ``` Note that this example uses Python 3.3 because that's where shutil.chown makes an appearance. This approach should work with any Python version that supports dictConfig - namely, Python 2.7, 3.2 or later. With pre-3.3 versions, you would need to implement the actual ownership change using e.g. os.chown. In practice, the handler-creating function may be in a utility module somewhere in your project. Instead of the line in the configuration where project.util can be replaced with the actual name of the package where the function resides. In the above working script, using 'ext://main.owned_file_handler' should work. Here, the actual callable is resolved by dictConfig from the ext:// specification. This example hopefully also points the way to how you could implement other types of file change - e.g. setting specific POSIX permission bits - in the same way, using os.chmod. Of course, the approach could also be extended to types of handler other than a ~logging.FileHandler - for example, one of the rotating file handlers, or a different type of handler altogether. Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.