This test failure occurs on Windows XP (x86) with 2.6.3.rc1

======================================================================
ERROR: Test seek/tell using the StatefulIncrementalDecoder.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Python26\lib\test\test_io.py", line 1063, in testSeekAndTell
    testSeekAndTellWithData(input)
  File "C:\Python26\lib\test\test_io.py", line 1043, in
testSeekAndTellWithData
    decoded = f.read()
  File "C:\Python26\lib\io.py", line 1725, in read
    decoder = self._decoder or self._get_decoder()
  File "C:\Python26\lib\io.py", line 1514, in _get_decoder
    decoder = make_decoder(self._errors)
  File "C:\Python26\lib\test\test_io.py", line 636, in __init__
    codecs.IncrementalDecoder.__init__(self, errors)
AttributeError: 'NoneType' object has no attribute 'IncrementalDecoder'

This is something that sometimes happens when running the test suite due
to module initialization or finalization oddities (I don't understand
the precise reasons myself). It isn't specific to test_io, I think.

Same error here:
http://www.python.org/dev/buildbot/builders/AMD64 Ubuntu 2.6/builds/555/steps/test/logs/stdio

(codecs_none.txt is a copy of stdio)

This issue is specific to Python 2.6. It can be reproduced with:

./python -E -tt ./Lib/test/regrtest.py -l -w test_pep263 test_operator test_asynchat test_zipimport_support test_pydoc test_code test_dis test_quopri test_doctest test_class test_sax test_fileio test_asyncore test_mailbox test_abstract_numbers test_uuid test_io test_enumerate test_property test_codecs

Or with this little test case:
----
import codecs, _codecs, sys, encodings

encoding = "cp1252"

codec = _codecs.lookup(encoding)

modname = 'encodings.%s' % encoding
__import__(modname)
del sys.modules[modname]
delattr(encodings, encoding)

encoder = codecs.getincrementalencoder(encoding)()
encoder.encode("", True)
----

module_dealloc() was modified in python trunk: the dictionary is only cleared if the reference counter is equal to 1.

/* If we are the only ones holding a reference, we can clear the dictionary. */
if (Py_REFCNT(m->md_dict) == 1) _PyModule_Clear((PyObject *)m);

module-dealloc() was changed by #7140 by r75437: "imp.new_module does not function correctly if the module is returned from a function and used directly".

Can we backport the fix to 2.6? It would be complex to write a workaround in the tests.

Here is a workaround. I didn't expected a short patch, but it's enough.

> Can we backport the fix to 2.6?

It's too late to fix such subtle bug in module machinery, so I commited my workaround in regrtest.py: r80538. Wait for the buildbots before closing the issue.

test_io and/or test_codecs failed on buildbots:
 - AMD64 Ubuntu 2.6 (r80535)
 - x86 Tiger 2.6 (r80535)
 - x86 Windows7 2.6 (r80531)

test_io and test_codecs didn't fail in the last build of x86 Tiger 2.6 and x86 Windows7 2.6. I suppose that the issue is now closed. Repopen the issue if it's not the case.