Issue #18345: Added cookbook example illustrating handler customisation.

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Vinay Sajip 2013-11-05 10:02:21 +00:00
parent 5c81164077
commit 2c1adcb62b
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@ -1694,3 +1694,138 @@ When the above script is run, it prints::
Note that the order of items might be different according to the version of
Python used.
.. currentmodule:: logging.config
Customising handlers with :func:`dictConfig`
--------------------------------------------
There are times when you want to customise logging handlers in particular ways,
and if you use :func:`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 :func:`shutil.chown`, but the file
handlers in the stdlib don't offer built-in support. You can customise handler
creation using a plain function such as::
def owned_file_handler(filename, mode='a', encoding=None, owner=None):
if owner:
if not os.path.exists(filename):
open(filename, 'a').close()
shutil.chown(filename, *owner)
return logging.FileHandler(filename, mode, encoding)
You can then specify, in a logging configuration passed to :func:`dictConfig`,
that a logging handler be created by calling this function::
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'formatters': {
'default': {
'format': '%(asctime)s %(levelname)s %(name)s %(message)s'
},
},
'handlers': {
'file':{
# The values below are popped from this dictionary and
# used to create the handler, set the handler's level and
# its formatter.
'()': owned_file_handler,
'level':'DEBUG',
'formatter': 'default',
# The values below are passed to the handler creator callable
# as keyword arguments.
'owner': ['pulse', 'pulse'],
'filename': 'chowntest.log',
'mode': 'w',
'encoding': 'utf-8',
},
},
'root': {
'handlers': ['file'],
'level': 'DEBUG',
},
}
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``::
import logging, logging.config, os, shutil
def owned_file_handler(filename, mode='a', encoding=None, owner=None):
if owner:
if not os.path.exists(filename):
open(filename, 'a').close()
shutil.chown(filename, *owner)
return logging.FileHandler(filename, mode, encoding)
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'formatters': {
'default': {
'format': '%(asctime)s %(levelname)s %(name)s %(message)s'
},
},
'handlers': {
'file':{
# The values below are popped from this dictionary and
# used to create the handler, set the handler's level and
# its formatter.
'()': owned_file_handler,
'level':'DEBUG',
'formatter': 'default',
# The values below are passed to the handler creator callable
# as keyword arguments.
'owner': ['pulse', 'pulse'],
'filename': 'chowntest.log',
'mode': 'w',
'encoding': 'utf-8',
},
},
'root': {
'handlers': ['file'],
'level': 'DEBUG',
},
}
logging.config.dictConfig(LOGGING)
logger = logging.getLogger('mylogger')
logger.debug('A debug message')
To run this, you will probably need to run as ``root``::
$ 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 :func:`shutil.chown`
makes an appearance. This approach should work with any Python version that
supports :func:`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.
:func:`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::
'()': owned_file_handler,
you could use e.g.::
'()': 'ext://project.util.owned_file_handler',
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 :func:`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 :func:`os.chmod`.
Of course, the approach could also be extended to types of handler other than a
:class:`~logging.FileHandler` - for example, one of the rotating file handlers,
or a different type of handler altogether.