[Python-Dev] Suspect intermittent failure in buildbots

[Amaury Forgeot d'Arc]

I've noticed an error that comes up from time to time in python 3.0 buildbots.
The error is always similar to this one:

Traceback (most recent call last):
  File "E:\cygwin\home\db3l\buildarea\3.0.bolen-windows\build\lib\test\test_io.py",
line 900, in testBasicIO
    self.assertEquals(f.write("abc"), 3)
  File "E:\cygwin\home\db3l\buildarea\3.0.bolen-windows\build\lib\io.py",
line 1486, in write
    b = encoder.encode(s)
  File "E:\cygwin\home\db3l\buildarea\3.0.bolen-windows\build\lib\encodings\ascii.py",
line 22, in encode
    return codecs.ascii_encode(input, self.errors)[0]
AttributeError: 'NoneType' object has no attribute 'ascii_encode'

The most recent is here:
http://www.python.org/dev/buildbot/3.0/AMD64%20W2k8%203.0/builds/843/step-test/0

but this already happened on various buildbots:
http://www.google.fr/search?q=%27NoneType%27+object+has+no+attribute+encode+site:mail.python.org/pipermail/python-checkins&filter=0

"x86 XP-4 3.0", "amd64 gentoo 3.0", "AMD64 W2k8 3.0", "x86 W2k8 3.0",
"g4 osx.4 3.0", "OS X x86 3.0"
"x86 XP-3 trunk"

yes, even on trunk!
Every time, a "codecs" global module variable has been reset to None,
either in a codec module (encoding/ascii.py, encoding/mac_roman.py) or
in test_io.py.
Every time, io.py is not far (which may be normal, it must have the
larger usage of encodings written in a .py)

I know that modules globals are reset to None on interpreter shutdown,
but it does not seem to be the case here: the unit test fail, and
fails again when run in verbose mode at the end.

I checked that the "codecs" name is a module global: the disassembler
shows a LOAD_GLOBAL opcode followed by LOAD_ATTR:
   0 LOAD_GLOBAL              0 (codecs)
   3 LOAD_ATTR                1 (ascii_decode)
   ...

I fail to imagine a reason, apart from a creeping memory error (in
dictionary lookup; chilling idea).
Thoughts?

-- 
Amaury Forgeot d'Arc