Hello.
I noticed strange behavior of logging module, when debugging my code:

$ python
Python 2.7.3 (default, Aug  1 2012, 05:14:39) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import logging
>>> logging.error('asdf')
ERROR:root:asdf
>>> logging.error('asdf', extra={'msg':123})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/logging/__init__.py", line 1575, in error
    root.error(msg, *args, **kwargs)
  File "/usr/lib/python2.7/logging/__init__.py", line 1166, in error
    self._log(ERROR, msg, args, **kwargs)
  File "/usr/lib/python2.7/logging/__init__.py", line 1257, in _log
    record = self.makeRecord(self.name, level, fn, lno, msg, args, exc_info, func, extra)
  File "/usr/lib/python2.7/logging/__init__.py", line 1235, in makeRecord
    raise KeyError("Attempt to overwrite %r in LogRecord" % key)
KeyError: "Attempt to overwrite 'msg' in LogRecord"


Originally code was extra=locals() and 'msg' was local variable, but it doesn't matter.

The issue is covered by the docs:

http://docs.python.org/2.7/library/logging.html#logging.Logger.debug

> The keys in the dictionary passed in extra should not clash with the keys used by the logging system.

You can't use a couple of reserved keys like 'msg' in the extra args. Perhaps you can find a simple workaround for your issue?