[Python-Dev] Bizarre new test failure

[Tim Peters]

Guido noticed this on Linux late this afternoon.  I've seen it on Win2K and
Win98SE since.  test_gc fails if you run the whole test suite from the
start:

test test_gc failed -- test_list: actual 10, expected 1

This seems impossible (look at the test).  It doesn't fail in isolation.  It
fails in both debug and release builds.  Not *all* tests before test_gc need
to be run in order to provoke a failure, but I can detect no sense in which
do need to be run (not just one or two, but lots of them).

Here are the files that changed between a Python that does work (yesterday)
and now:

P python/configure
P python/configure.in
P python/pyconfig.h.in
P python/Doc/lib/libgetopt.tex
P python/Doc/lib/libsocket.tex
P python/Lib/copy.py
P python/Lib/fileinput.py
P python/Lib/getopt.py
P python/Lib/posixpath.py
P python/Lib/shutil.py
P python/Lib/socket.py
P python/Lib/compiler/pyassem.py
P python/Lib/compiler/pycodegen.py
P python/Lib/compiler/transformer.py
P python/Lib/distutils/command/clean.py
P python/Lib/test/test_b1.py
P python/Lib/test/test_commands.py
P python/Lib/test/test_descr.py
P python/Lib/test/test_getopt.py
P python/Lib/test/test_socket.py
U python/Lib/test/test_timeout.py
P python/Misc/ACKS
P python/Misc/NEWS
P python/Modules/gcmodule.c
P python/Modules/socketmodule.c
P python/Modules/socketmodule.h
P python/Objects/abstract.c
P python/Objects/complexobject.c
P python/Objects/rangeobject.c
P python/Tools/webchecker/webchecker.py

While Jeremy did fiddle gcmodule.c, that isn't the cause.

I changed the test like so:

def test_list():
    import sys
    l = []
    l.append(l)
    gc.collect()
    del l
    gc.set_debug(gc.DEBUG_SAVEALL)
    n = gc.collect()
    print >> sys.stderr, '*' * 30, n, gc.garbage
    expect(n, 1, "list")

Here's the list of garbage objects it found:

[<class 'test_descr.mysuper'>,
 {'__dict__': <attribute '__dict__' of 'mysuper' objects>,
 '__module__': 'test_descr',
 '__weakref__': <member '__weakref__' of 'mysuper' objects>,
 '__doc__': None,
 '__init__': <function __init__ at 0x00CC00D8>},
 (<class 'test_descr.mysuper'>, <type 'super'>, <type 'object'>),
 (<type 'super'>,),
 [[...]],
 <attribute '__dict__' of 'mysuper' objects>,
 <member '__weakref__' of 'mysuper' objects>,
 <function __init__ at 0x00CC00D8>,
 (<cell at 0x00CB4DB0: type object at 0x00768420>,),
 <cell at 0x00CB4DB0: type object at 0x00768420>]

The recursive list:

 [[...]]

is the only one expected here.

Your turn <wink>.