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"python -m test test_packaging test_zipimport" fails with:
======================================================================
FAIL: testAFakeZlib (test.test_zipimport.CompressedZipImportTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/haypo/prog/HG/cpython/Lib/test/test_zipimport.py", line 130, in testAFakeZlib
 self.fail("expected test to raise ImportError")
AssertionError: expected test to raise ImportError
The problem is that the zipimport module keeps a reference to zlib.decompress() which "makes zlib.decompress immortal": see get_decompress_func() in zipimport.c.
Attached patch replaces the borrowed reference by a classic reference to allow to unload zlib.
I don't think that it makes zipimport slower: it calls PyImport_ImportModuleNoBlock("io") and PyObject_GetAttrString(zlib, "decompress") each time instead of just once, but PyImport_ImportModuleNoBlock() is just a lookup in a dict (if the zlib module is not unloaded between two calls to get_data()).

OMG! I understood why the bug was not seen before: "python -m test test_zipimport test_zipimport" succeed because test_zipimport REMOVES testAFakeZlib tests after the first run!
New patch to remove this ugly hack (it is no more needed with my patch anyway).

"test_zipimport REMOVES testAFakeZlib tests after the first run" hack was introduced by a commit supposed to "test zipimport a bit more" :-)
changeset: 36383:7b3d915b6e9d
branch: legacy-trunk
user: Neal Norwitz <nnorwitz@gmail.com>
date: Mon Jan 23 07:52:13 2006 +0000
files: Lib/test/test_zipimport.py
description:
Test zipimporter a bit more. Also get working with -R :: option for finding ref leaks

New changeset 52d9183b34f8 by Victor Stinner in branch '3.1':
Issue #12124: zipimport doesn't keep a reference to zlib.decompress() anymore
http://hg.python.org/cpython/rev/52d9183b34f8
New changeset a043d8e168b3 by Victor Stinner in branch '3.2':
(Merge 3.1) Issue #12124: zipimport doesn't keep a reference to
http://hg.python.org/cpython/rev/a043d8e168b3
New changeset 9e13869b7639 by Victor Stinner in branch 'default':
(Merge 3.2) Issue #12124: zipimport doesn't keep a reference to
http://hg.python.org/cpython/rev/9e13869b7639 

New changeset bfceb8c8178a by Victor Stinner in branch '2.7':
Issue #12124: zipimport doesn't keep a reference to zlib.decompress() anymore
http://hg.python.org/cpython/rev/bfceb8c8178a