The following code reproduces the error:

import logging
logging.root.addHandler(logging.FileHandler(filename='test.log',encoding='UTF16'))
logging.error( u'b\u0142\u0105d')

I think the problem is in the line
logging/__init__.py:860: ufs = fs.decode(stream.encoding)

as Python can't really handle the following code:

fs = "%s\n"
print fs.decode('utf16') % u'foo'

The example works fine on Python3:

localhost$ python3
Python 3.3.2 (default, Aug 23 2013, 19:00:04) 
[GCC 4.8.1 20130603 (Red Hat 4.8.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import logging
>>> logging.root.addHandler(logging.FileHandler(filename='test.log',encoding='UTF16'))
>>> logging.error( u'b\u0142\u0105d')
>>> 

localhost$ hexdump test.log
0000000 feff 0062 0142 0105 0064 000a          
000000c

I don't understand the purpose of fs.decode(stream.encoding): why not directly using ufs=u'%s\n"?

@Pawel: Can you please try to replace ufs=fs.decode(stream.encoding) with ufs=u'%s\n'?

Hi Victor. Your fix works, but actually using simply ufs='%s\n' also seem to work, as 
type( '%s' % u'foo')
and 
type( u'%s' % u'foo')
returns the same - unicode. 

So I would suggest dropping ufs completely, and changing the two occurences to fs. It works - I checked. Maybe some code refactoring could be done then, as I'm not sure if the two nested 'try' statements are needed in such case.

Btw I also don't see the purspose of fs.decode(stream.encoding), as it should rather be encoded and not decoded...

Hi,

here the patch to fix this bug on Python 2.7 with a test suite.

patch_utf16 looks good to me.

New changeset e94e29dab32c by Victor Stinner in branch '2.7':
Close #19267: Fix support of multibyte encoding (ex: UTF-16) in the logging
http://hg.python.org/cpython/rev/e94e29dab32c

This bug is specific to Python 2. I should now be fixed, thanks Paweł for the report and Natal for the patch.

@Natal: Could you please sign the Contributor Agreement for next contributions?
http://www.python.org/psf/contrib/contrib-form/

Cool - looks good to me as well. Thanks guys.