settings.py gets imported twice

Hi,

settings.py gets imported twice. This is bad, if you want
to
set up the logging module, since you register the handler
twice
and you get all log messages twice.

Here are the stacktraces I created for debugging this:

===> python manage.py test admin
import logconfig
Traceback (most recent call last):
  File "manage.py", line 12, in ?
    import settings # Assumed to be in the same directory.


Traceback (most recent call last):
  File "manage.py", line 19, in ?
    execute_manager(settings)
  File
"/localhome/user/myproject/django/core/management/__ini
t__.py", line 277, in execute_manager
    utility.execute()
  File
"/localhome/user/myproject/django/core/management/__ini
t__.py", line 225, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File
"/localhome/user/myproject/django/core/management/__ini
t__.py", line 177, in fetch_command
    self.project_directory)[subcommand]
  File
"/localhome/user/myproject/django/core/management/__ini
t__.py", line 86, in get_commands
    for app_name in settings.INSTALLED_APPS:
  File
"/localhome/user/myproject/django/conf/__init__.py"
;, line 28, in __getattr__
    self._import_settings()
  File
"/localhome/user/myproject/django/conf/__init__.py"
;, line 57, in _import_settings
    self._target = Settings(settings_module)
  File
"/localhome/user/myproject/django/conf/__init__.py"
;, line 83, in __init__
    mod = __import__(self.SETTINGS_MODULE, {}, {}, [''])
  File "/localhome/user/myproject/settings.py",
line 147, in ?

This shnippet has a workaround:
  http://www
.djangosnippets.org/snippets/16/
(I have not tested it yet)

I think it would be better to avoid a second import.

Any hints?

 Thomas

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On Mon, 2007-11-05 at 10:46 +0100, Thomas Güttler wrote:
> Hi,
> 
> settings.py gets imported twice. This is bad, if you
want to
> set up the logging module, since you register the
handler twice
> and you get all log messages twice.
[...]

It's actually fairly hard to avoid this for a variety of
reasons. I
think we used to import it more than twice in some
situations. Maybe we
still do. User-defined commands and processing the
--settings option
becomes more fiddly, for example. So the answer is
"don't rely on it
only being imported once".

If you need something to be only done once, no matter how
many times it
is imported, you will need to set a flag somewhere. For
example, you
could set a global variable that indicates you have already
set up your
logging. Or set an indicator on some other class.

For logging, I would think that a call to getLogger('name')
would
probably do the trick. If it returns nothing, you still need
to do the
setup.

Regards,
Malcolm

-- 
If it walks out of your refrigerator, LET IT GO!! 
http://www.pointy-s
tick.com/blog/


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Am Montag, 5. November 2007 10:55 schrieb Malcolm
Tredinnick:
> On Mon, 2007-11-05 at 10:46 +0100, Thomas Güttler
wrote:
> > Hi,
> >
> > settings.py gets imported twice. This is bad, if
you want to
> > set up the logging module, since you register the
handler twice
> > and you get all log messages twice.
>
> [...]
>
> It's actually fairly hard to avoid this for a variety
of reasons. I
> think we used to import it more than twice in some
situations. Maybe we
> still do. User-defined commands and processing the
--settings option
> becomes more fiddly, for example. So the answer is
"don't rely on it
> only being imported once".

OK,

maybe it should be documented.

The usual way to use global variables with a different
module:
http://effbot.org/pyfaq/how-do-i-share
-global-variables-across-modules.htm

did not work for me, since the modul gets imported with
different __name__'s.

The first time __name__ is 'logconfig' the second time it is

'myproject.logconfig'.


A found this solution.

# file logconfig.py
import logging
if not hasattr(logging, "set_up_done"):
    logging.set_up_done=False

def set_up(myhome):
    if logging.set_up_done:
        return
    logging.set_up_done=True


 Thomas

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Thomas Guettler wrote:
> A found this solution.
>
> # file logconfig.py
> import logging
> if not hasattr(logging, "set_up_done"):
>     logging.set_up_done=False
>
> def set_up(myhome):
>     if logging.set_up_done:
>         return
>     logging.set_up_done=True
>   
Here's an alternative solution - it's based on the idea that
the 
handlers are added to the logger only once. (getLogger
returns the same 
logger instance each time).

import logging
logger=logging.getLogger("dws")
if not logger.handlers:
    ...
    logger.addHandler(....)




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Am Dienstag, 6. November 2007 07:00 schrieb Matti Haavikko:
> Here's an alternative solution - it's based on the idea
that the
> handlers are added to the logger only once. (getLogger
returns the same
> logger instance each time).
>
> import logging
> logger=logging.getLogger("dws")
> if not logger.handlers:
>     ...
>     logger.addHandler(....)

Hi,

I used something like this, but used the root logger
(getLogger()).

If there is a call to logging.log(...) before you add your
handler,
python automatically inserts one for you. This means the
if-statement
above will be false (and addHandler() would not be called),
even on the first 
run.

 Thomas



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