Issue 11089 submitted a patch to 3.2 and 2.7 to address performance concerns with the latest updates to ConfigParser.  In the implementation for 2.7.2, this patch was misapplied in the keys() function on line 573:

  for mapping in self_maps:

should be:

  for mapping in self._maps:

As a result the following raises a NameError:

>>> import ConfigParser
>>> ConfigParser._Chainmap()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\UserDict.py", line 172, in __repr__
    return repr(dict(self.iteritems()))
  File "C:\Python27\lib\UserDict.py", line 110, in iteritems
    for k in self:
  File "C:\Python27\lib\UserDict.py", line 97, in __iter__
    for k in self.keys():
  File "C:\Python27\lib\ConfigParser.py", line 573, in keys
    for mapping in self_maps:
NameError: global name 'self_maps' is not defined

Thanks for catching this.  I’m baffled that the test suite did not catch that.

Thanks, I'll fix that shortly.

New changeset 7d5a37ce42d5 by Raymond Hettinger in branch '2.7':
Issue 12717: Fix-up an earlier backport in ConfigParser.
http://hg.python.org/cpython/rev/7d5a37ce42d5

Fixed.  Thanks for the report.

Éric, the test suite didn't catch this because the error wasn't user visible -- the chainmap is only used internally and only __getitem__ was needed.

Happy to help!

Raymond - I came across this issue while reviewing notes from your OSCON Advanced Python talk - thanks for the great tutorial!