logging package problems

[Robert.Schmitt at cellzome.com]

I found that the configuration system of the new logging package of Python 
2.3 has some 
unintuitive idiosyncracies that are worth mentioning because they can cost 
you quite some 
development time and are not documented elsewhere.

I used the logging configuration file shown below. My aim was to log only 
the INFO messages,
but log DEBUG messages for one particular module (called webTestLogin.py).

Here's what I found out:
- if your init logging in your module with the line
        log = logging.getLogger()
  then the logging module will determine the module where the call 
originated and in your log files
  you'll find lines like
        2004-01-26 11:21:15,890 [INFO] creating ticket for this session 
[in webtestlogin]
  where webTestLogin mysteriously lost its capitalization. Now, this does 
*not* mean that
  webtestlogin will also be the 'qualname', i.e. the name of a channel 
that you can use
  to log messages from this module to a different place or in a different 
manner; for that
  to work, you'll need the following line of code:
        log = logging.getLogger('webtestlogin')
  (making 'webtestlogin' a channel, or some sort of logical logging unit 
that allow its calls to be handled
  differently from the other log calls in your program).
  The documentation says qualname is the 'fully qualified name', but 
doesn't contend on what
  that is; I tried the complete package name, that didn't work 
('com.cellzome.pandora.webTestLogin').
- capitalization *is* very important; if you use lowercase in the code, 
you'll need lowercase
  in the logging config file as well (see the qualname line below)
- 'propagate' forwards log messages to other loggers, so you may e.g. log 
the same line to
  two different places - so far so good. But: If you set propagate to 1 in 
the [logger_webtestlogin]
  shown below, the root logger will log DEBUG messages too, even though it 
was told to log
  only INFO - just because the message has been forwarded (?!?)
  Generally I think that propagation follows the order of the loggers, but 
I still don't get the
  complete picture.
- the config file scanner/parser is not very robust; if you use spaces in 
a list for aesthetic reasons
  (e.g. keys=root, webtestlogin) the key list will be ('root', ' 
webtestlogin'). This can produce
  quite esoteric errors :-)

Maybe I didn't get the point/purpose of the framework on some of those 
issues, but
then again it might be worth to extend the existing documentation a bit.

Cheers,

Robert F Schmitt, Cellzome AG
Meyerhofstr. 1, D-69117 Heidelberg, Germany
Tel + 49 6221 137 57 405, Fax + 49 6221 137 57 202
www.cellzome.de
------------------------------------------------------------------------------------
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- George W. Bush

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- George W. Bush

///////////////////////////////////////////////////////////////////
///////////////           config file             ///////////////
///////////////////////////////////////////////////////////////////

###########################################################
# general references

[loggers]
keys=root,webtestlogin

[handlers]
keys=drogenHandler,stdoutHandler

[formatters]
keys=taschenFormat,textOnlyFormat

###########################################################
# loggers

[logger_webtestlogin]
level=DEBUG
handlers=drogenHandler,stdoutHandler
propagate=0
qualname=webtestlogin

[logger_root]
level=INFO
handlers=drogenHandler,stdoutHandler
propagate=1

###########################################################
# handlers

[handler_drogenHandler]
class=FileHandler
level=NOTSET
formatter=taschenFormat
args=('pandora.log', 'w')

[handler_stdoutHandler]
class=StreamHandler
level=INFO
formatter=textOnlyFormat
args=(sys.stdout,)

###########################################################
# formatters

[formatter_taschenFormat]
format=%(asctime)s [%(levelname)s] %(message)s [in %(module)s]

[formatter_textOnlyFormat]
format=%(levelname)s %(message)s

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