How to prevent logging warning?

[Thomas Heller]

I'm about to add some logging calls to a library I have. How can I
prevent that the script that uses the library prints
'No handlers could be found for logger "comtypes.client"' when the
script runs?

I would like to setup the logging so that there is no logging when
nothing is configured, and no warning messages are printed.

Thomas

 

[Maksim Kasimov]

may be this you will find usefull:

def getLog(logName, fileName = None):

if fileName:
hdl = logging.FileHandler(fileName)
else:
hdl = logging.StreamHandler()

fmt = logging.Formatter("%(name)s:\t%(levelname)s:\t%(asctime)s:\t%(message)s")
hdl.setFormatter(fmt)
log = logging.getLogger(logName)
log.addHandler(hdl)

return log

 

[Thomas Heller]

may be this you will find usefull:

def getLog(logName, fileName = None):

if fileName:
hdl = logging.FileHandler(fileName)
else:
hdl = logging.StreamHandler()

fmt = logging.Formatter("%(name)s:\t%(levelname)s:\t%(asctime)s:\t%(message)s")
hdl.setFormatter(fmt)
log = logging.getLogger(logName)
log.addHandler(hdl)

return log

Not really - I know how to set up handlers, but I think it should be
optional. Assume I have

log = logging.getLogger("comtypes.client")

and later

log.warn("foo bar")

in the library code.

If I use the library an my script, I get the warning that I mentioned
above. I want the script by default to be agnostic about the libraries
logging. When I want to see the log messages, I can always do

logging.basicConfig()

in the script to see the log messages.

I get the behaviour that I want when I add a 'NULL' handler in the
library, but is this really how logging is intended to be used?

<library>
log = logging.getLogger("comtypes.client")

class NULLHandler(logging.Handler):
def emit(self, *args):
pass

log.addHandler(NULLHandler())
</library>

Thomas

 

[Neil Benn]

Not really - I know how to set up handlers, but I think it should be
optional. Assume I have

log = logging.getLogger("comtypes.client")

and later

log.warn("foo bar")

in the library code.

If I use the library an my script, I get the warning that I mentioned
above. I want the script by default to be agnostic about the libraries
logging. When I want to see the log messages, I can always do

logging.basicConfig()

in the script to see the log messages.

I get the behaviour that I want when I add a 'NULL' handler in the
library, but is this really how logging is intended to be used?

<library>
log = logging.getLogger("comtypes.client")

class NULLHandler(logging.Handler):
def emit(self, *args):
pass

log.addHandler(NULLHandler())
</library>

Thomas

Hello,

Absolutley not, I have exactly the same problem and it is
really annoying. The logging handlers should be set from an external
config file and not explicitly in the code. I simply had to just live
with it, it's annoying but there is nothing you can do about it (short
of playing around with stdout but avoiding that is why you used logging
in the first place!).

Cheers,

Neil

--

Neil Benn
Senior Automation Engineer
Cenix BioScience
BioInnovations Zentrum
Tatzberg 46
D-01307
Dresden
Germany

Tel : +49 (0)351 4173 154
e-mail : (e-mail address removed)
Cenix Website : http://www.cenix-bioscience.com

 

[Trent Mick]

[Thomas Heller wrote]

I'm about to add some logging calls to a library I have. How can I
prevent that the script that uses the library prints
'No handlers could be found for logger "comtypes.client"' when the
script runs?

I would like to setup the logging so that there is no logging when
nothing is configured, and no warning messages are printed.

This is probably a gross hack, but then I think one could argue that the
one-time "No handlers could be found for" warning is a misfeature -- at
least without a clean way to suppress it. I don't know the history of
that warning though:


-------------- mylib.py -----------------------
import logging
log = logging.getLogger("mylib")
def func():
log.warn("don't go near the river")
log.error("I'm drowning!")
--------------------------------------------------


-------------- myscript.py -----------------------
import sys
import logging
import mylib

if __name__ == "__main__":
if "-v" in sys.argv:
logging.basicConfig()
else:
logging.Logger.manager.emittedNoHandlerWarning = True
mylib.func()
--------------------------------------------------


$ python myscript.py

$ python myscript.py -v
WARNING:mylib:don't go near the river
ERROR:mylib:I'm drowning!


hackily yours,
Trent

 

[Peter Otten]

I want the script by default to be agnostic about the libraries
logging.  When I want to see the log messages, I can always do

logging.basicConfig()

in the script to see the log messages.

I get the behaviour that I want when I add a 'NULL' handler in the
library, but is this really how logging is intended to be used?

I would support ...err, what's the opposite of a feature request?
Anyway, another hack, slightly more lightweight/intrusive:

logging.root.manager.emittedNoHandlerWarning = True

Peter

 

[Vinay Sajip]

I get the behaviour that I want when I add a 'NULL' handler in the
library, but is this really how logging is intended to be used?

The reason for the one-off message is that without it, a
misconfiguration or a failure to configure any handlers is notified to
a user (who is possibly not used to the logging package). I'm not sure
which is more annoying - a one-off message which occurs when no
handlers are configured and yet events are logged, or complete silence
from logging when something is misconfigured, and not giving any
feedback on what's wrong? (It's a rhetorical question - the answer is
of course quite subjective).

Certainly, I could change things so that e.g. the error is suppressed
when logging.raiseExceptions is set to 0 (typically for production
use).

Regards,

Vinay Sajip

 

[Vinay Sajip]

s/without/with/

 

[Thomas Heller]

The reason for the one-off message is that without it, a
misconfiguration or a failure to configure any handlers is notified to
a user (who is possibly not used to the logging package). I'm not sure
which is more annoying - a one-off message which occurs when no
handlers are configured and yet events are logged, or complete silence
from logging when something is misconfigured, and not giving any
feedback on what's wrong? (It's a rhetorical question - the answer is
of course quite subjective).

I do *not* think 'no handler' is a misconfiguration. Is it possible to
differentiate between a misconfiguration and 'no configuration'?

Certainly, I could change things so that e.g. the error is suppressed
when logging.raiseExceptions is set to 0 (typically for production
use).

That would be fine. But there are also other ways - you could, for
example, print the warning only when __debug__ is False. And you could
use the warnings module instead of blindly printing to stderr, this way
it could also be filtered out.

BTW: Since I have your attention now, is the graphical utility to
configure the logging.conf file still available somewhere, and
compatible with the current logging package (with 'current' I mean
the one included with Python 2.3.5)?

Thomas

 

[Vinay Sajip]

I do *not* think 'no handler' is a misconfiguration. Is it possible to
differentiate between a misconfiguration and 'no configuration'?

It's a fair point. The line was more blurred when the logging package
was newly released into the wild ;-) But "no configuration" could be
caused e.g. by an unreadable config file, which might also be
categorised as a "misconfiguration".

That would be fine. But there are also other ways - you could, for
example, print the warning only when __debug__ is False. And you could
use the warnings module instead of blindly printing to stderr, this way
it could also be filtered out.

Compatibility with 1.5.2 precludes use of the warnings module. If using
raiseExceptions meets your requirement, I'll use that. I'm not sure
it's a good idea for the behaviour to change between running with and
without -O.

BTW: Since I have your attention now, is the graphical utility to
configure the logging.conf file still available somewhere, and
compatible with the current logging package (with 'current' I mean
the one included with Python 2.3.5)?

You can always get my attention via email The graphical utility
(logconf.py) is available from the download at

http://www.red-dove.com/python_logging.html#download

AFAIK it should work OK with 2.3.5, though I haven't tested it recently
as there wasn't much interest in it. In fact you're the first person to
ask! It generates a few extra entries in the config file which are used
by the utility only, which are seemingly regarded as "cruft" by most
people.

Regards,


Vinay Sajip

 

[Vinay Sajip]

I have now checked a change into CVS whereby the one-off error message
is not printed unless raiseExceptions is 1. The default behaviour is
thus unchanged, but if you set raiseExceptions to 0 for production use
and then don't configure any handlers, then the message is not printed.

Regards,

Vinay Sajip