Antoine, I committed your patch (with a bit of comments added), *leaving the module caching in*. This is because removing it breaks the tests, unfortunately. The _elementtree tests are so crooked that they manage to create a situation in which the module under test throws ParseError which is a different class from ET.ParseError. This is "achieved" by multiple invocations of import_fresh_module with various fresh & blocked parameters, and I still haven't fully traced all the problems yet. Since this caching only potentially harms other tests, it's ok to leave in.

A longer term solution to all this will be http://mail.python.org/pipermail/python-dev/2013-August/127766.html - I want to eventually run all "monkey-patch the import environment to simulate some situation" sub-tests of ET in different subprocesses to they are kept independent.