python locale strange error. what's going on here exactly?

Question

So today I upgraded to bazaar 2.0.2, and I started receiving this message (I'm on snow leopard, btw):

bzr: warning: unknown locale: UTF-8
  Could not determine what text encoding to use.
  This error usually means your Python interpreter
  doesn't support the locale set by $LANG (en_US.UTF-8)
  Continuing with ascii encoding.

very strange, since my LANG is actually empty. Similar thing happen when I try to tinker with the locale module

Python 2.5.4 (r254:67916, Nov 30 2009, 14:09:22) 
[GCC 4.3.4] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import locale
>>> locale.getdefaultlocale()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sbo/runtimes/lib/python2.5/locale.py", line 443, in getdefaultlocale
    return _parse_localename(localename)
  File "/Users/sbo/runtimes/lib/python2.5/locale.py", line 375, in _parse_localename
    raise ValueError, 'unknown locale: %s' % localename
ValueError: unknown locale: UTF-8

exporting LANG does not help

sbo@dhcp-045:~ $ export LANG=en_US.UTF-8
sbo@dhcp-045:~ $ bzr
bzr: warning: unknown locale: UTF-8
  Could not determine what text encoding to use.
  This error usually means your Python interpreter
  doesn't support the locale set by $LANG (en_US.UTF-8)
  Continuing with ascii encoding.

However, this solved the problem

sbo@dhcp-045:~ $ export LANG=en_US.UTF-8
sbo@dhcp-045:~ $ export LC_ALL=en_US.UTF-8

Python 2.5.4 (r254:67916, Nov 30 2009, 14:09:22) 
[GCC 4.3.4] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import locale
>>> locale.getdefaultlocale()
('en_US', 'UTF8')

Could you please explain what's going on here, for better googlability ?

Answer 1

2016 UPDATE: Turns out that this is a Python bug since at least 2013, very probably earlier too, consisting in Python not reacting well to non-GNU locales - like those found in Mac OS X and the BSDs. The bug is still open as of September 2016, and affects every Python version.

---

If there was no LANG environment variable set, chances are you had either an LC_CTYPE (the key variable) or LC_ALL (which overrides if set) environment variable set to UTF-8, which is not a valid OS X locale. It's easy enough to reproduce with the Apple-supplied /usr/bin/python or with a custom python, as in your case, that was built with the 10.6 SDK (probably also the 10.5 SDK). You won't be able to reproduce it that way with a python.org python; they are currently built with the 10.4 SDK where the locale APIs behave differently.

$ unset LANG
$ env | grep LC_
$ export LC_CTYPE="UTF-8"
$ /usr/bin/python  # Apple-supplied python
Python 2.6.1 (r261:67515, Jul  7 2009, 23:51:51) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import locale ; locale.getdefaultlocale()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/locale.py", line 459, in getdefaultlocale
    return _parse_localename(localename)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/locale.py", line 391, in _parse_localename
    raise ValueError, 'unknown locale: %s' % localename
ValueError: unknown locale: UTF-8
^D
$ /usr/local/bin/python2.6   # python.org python
Python 2.6.4 (r264:75821M, Oct 27 2009, 19:48:32) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import locale ; locale.getdefaultlocale()
(None, 'mac-roman')
>>> 

EDIT:

There may be another piece to the puzzle. A quick look at the bzr 2.0.1 I have installed indicates that the message you cite should only show up if locale.getpreferredencoding() raises a locale.Error. One way that can happen is if the python _locale.so C extension can't be loaded and that can happen if there are permission problems on it. For example, MacPorts currently is known to have problems setting permissions if you have a customized umask; I've been burned by that issue myself. Check the permissions of _locale.so in the python lib/python2.5/lib-dynload directory and ensure it is 755. The full path for MacPorts should be:

/opt/local/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/lib-dynload/