[New-bugs-announce] [issue2697] Logging ancestors ignored after configuration

[andrew cooke]

New submission from andrew cooke <andrew at acooke.org>:

I am seeing some odd behaviour with logging which would be explained
if loggers that are not defined explicitly (but which are controlled
via their ancestors) must be created after the logging system is
configured via fileConfig().

That's a bit abstract, so here's the problem itself:  I define my log
within a module by doing

import logging
log = logging.getLogger(__name__)

Now typically __name__ will be something like "acooke.utils.foo".

That happens before the application configures logging, which it does
by calling logging.config.fileConfig() to load a configuration.

If I do that, then I don't see any logging output from
"acooke.utils.foo" (when using "log" from above after "fileConfig" has
been called) unless I explicitly define a logger with that name.
Neither root nor an "acooke" logger, defined in the config file, are
called.

One way to handle this is to make creation of module-level Loggers
lazy, and make sure that logging initialisation occurs before any
other logging is actually used (which is not so hard - just init log
at the start of the application).

Of course, there's a performance hit...

For example:

class Log(object):
    def __init__(self, name):
        super(Log, self).__init__()
        self._name = name
        self._lazy = None
    def __getattr__(self, key):
        if not self._lazy:
            self._lazy = logging.getLogger(self._name)
        return getattr(self._lazy, key)

and then, in some module:

from acooke.util.log import Log
log = Log(__name__)
[...]
class Foo(object):
    def my_method(self):
        log.debug("this works as expected")

----------
components: Library (Lib)
messages: 65843
nosy: acooke
severity: normal
status: open
title: Logging ancestors ignored after configuration
type: behavior
versions: Python 2.5

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Tracker <report at bugs.python.org>
<http://bugs.python.org/issue2697>
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