Got some problems when using logging Filter

[Jean-Michel Pichavant]

sword wrote:
> On Nov 16, 7:40 pm, Jean-Michel Pichavant <jeanmic... at sequans.com>
> wrote:
>   
>> sword wrote:
>>     
>>> The logging cookbook gives an Filter example, explainning how to add
>>> contextural info to log. I can't figure out how to filter log from it.
>>>       
>>> Suppose I have 3 file, a.py, b.py and main.py
>>> #file: a.py
>>> import logging
>>>       
>>> logger=logging.getLogger(__name__)
>>> def print_log():
>>>     logger.debug("I'm module a")
>>>       
>>> #file: b.py just like a.py
>>> import logging
>>> logger=logging.getLogger(__name__)
>>> def print_log():
>>>     logger.debug("I'm module b")
>>>       
>>> #file: main.py
>>> import logging
>>> from logging import Filter
>>> logging.basicConfig(level=logging.DEBUG)
>>> logger=logging.getLogger("main")
>>> logger.debug("This is main process")
>>> logger.addFilter(Filter("a"))
>>>       
>>> And I expected that the console output would contain main and b module
>>> log only. But it turned out that all logs there.  Is it the problem of
>>> root logger?
>>>       
>> Hi,
>>
>> First of all, in the code you provided we can't see where you import a &
>> b, and when you call their respective print_log method.
>> Secondly,Filter("a") would allow only the "a" log events, not forbid
>> them. quoting the docs: "if name is specified, it names a logger which,
>> together with its children, will have its events allowed through the
>> filter."
>>
>> As for your problem it may come from the fact that you applied the
>> filter to the 'main' logger, while you probably want to add the filter
>> to the *root* logger. Your current hierarchy is
>>
>> root
>>   - main
>>   - a
>>   - b
>>
>> events fired from 'a' will be handled by the root logger, not the main.
>> root = logging.getLogger()
>> root.addFilter('main')
>> root.addFilter('a')
>> root.addFilter('b')
>>
>> JM
>>     
>
> Thanks for your reply. I tried to edit the source a bit, now the
> main.py looks like this:
> #main.py
> import logging
> from logging import Filter
> import a
> import b
>
> logging.basicConfig(level=logging.DEBUG)
> root = logging.getLogger()
> root.addFilter(Filter("GoneWithTheWind")) #so I suppose no log msg
> would pass this filter
>
> logger = logging.getLogger("main")
> logger.debug("main process")
> a.print_log()
> b.print_log()
>
> ####
> And It still prints out all the log msg. :(
>   
You need to add you filter to the handler(s) of the root logger, not the 
root logger itself.

Filters to loggger object are applied only when the log event is raised, 
i.e. when one of the logging method error, info, warning, debug is called.
In your case, log events are raised by other loggers than the root 
logger, so its filter will not apply.

However any filter applied to the root *handlers* will be applied to any 
log processed by the handler, including log event raised by sub-logger.

root.handlers[-1].addFilter(Filter("GoneWithTheWind")) #so I suppose no log msg

JM

Quoting http://docs.python.org/library/logging.html#filter-objects

"Note that filters attached to handlers are consulted whenever an event is emitted by the handler, whereas filters attached to loggers are consulted whenever an event is logged to the handler (using debug(), info(), etc.) This means that events which have been generated by descendant loggers will not be filtered by a logger’s filter setting, unless the filter has also been applied to those descendant loggers."