[Python-Dev] regrtest.py mystery

[Tim Peters]

[Fred]
>   Perhaps it should hold onto the module as well?  That would avoid it
> getting cleaned up before possibly dependent modules.
>   For the test case problem, perhaps there should be a list of
> exceptional modules that don't get cleaned up by regrtest once they
> appear.  encodings and warnings would probably both need to be on the
> list.  This list should probably be in the sys module; it would also
> be useful for the RollbackImporter in the unittestgui.py script that
> comes with the separate PyUnit package.

I expect the problem is intractable.  Here's a revealing experiment:  add
this block to the start of test___all__.check_all():

    if modname in sys.modules:
        del sys.modules[modname]

That is, just prior to test___all__ trying to import a module, remove *only*
that module from sys.modules if it's already there.  Sounds pretty harmless,
right?  But on Windows, it causes 28 standard tests to fail (possibly more
on Linux):

28 tests failed:
    test___all__ test_difflib test_email test_fileinput test_fnmatch
    test_future test_gettext test_glob test_global test_htmllib
    test_htmlparser test_inspect test_mimetypes test_mmap test_os
    test_pyclbr test_re test_regex test_repr test_scope test_sre
    test_strftime test_strop test_sundry test_tokenize test_urllib2
    test_xmllib test_xmlrpc

Trying to figure which modules "hurt" turns out to be a nightmare.  Here's
the minimal set that allows the test suite to pass again on Windows, using
the default test order:

    if modname in sys.modules:
        if modname not in (
"copy_reg",
"os",
"sgmllib",
"sre",
"tempfile",
"tokenize",
"warnings",
):
            del sys.modules[modname]

Am I gonna check that in?  Fat chance <wink>.