couple of new list.sort bugs

[mwhudson]

BPO	848856
Nosy	@mwhudson, @rhettinger
Files	list-nagery.diff: fix attempt Support "bpo-" in Misc/NEWS #1 list-nagery-2.diff: fix attempt Rename README to README.rst and enhance formatting #2

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/mwhudson'
closed_at = <Date 2003-12-04.11:26:39.000>
created_at = <Date 2003-11-25.11:12:33.000>
labels = ['interpreter-core']
title = 'couple of new list.sort bugs'
updated_at = <Date 2003-12-04.11:26:39.000>
user = 'https://github.com/mwhudson'

bugs.python.org fields:

activity = <Date 2003-12-04.11:26:39.000>
actor = 'mwh'
assignee = 'mwh'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2003-11-25.11:12:33.000>
creator = 'mwh'
dependencies = []
files = ['1113', '1114']
hgrepos = []
issue_num = 848856
keywords = []
message_count = 9.0
messages = ['19115', '19116', '19117', '19118', '19119', '19120', '19121', '19122', '19123']
nosy_count = 2.0
nosy_names = ['mwh', 'rhettinger']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue848856'
versions = ['Python 2.4']

[mwhudson]

I really feel I should apologise for this one:

[mwh@pc150 build-debug]$ cat t.py
class SortKiller(object):
def __init__(self, i):
pass
def __del__(self):
del l[:]

l = range(10)
l.sort(key=SortKiller)
[mwh@pc150 build-debug]$ ./python t.py
Segmentation fault

This can be fixed by moving the "restoring the objects
of the list from the wrappers" code *before* the "put
saved_ob_item back in the list" code.

The second is less serious but probably more annoying
to fix:

[mwh@pc150 build-debug]$ cat u.py
def k(x): return 1/x

l = range(-2,2)
try:
l.sort(key=k)
except ZeroDivisionError:
pass
print l
[mwh@pc150 build-debug]$ ./python u.py
[<sortwrapper object at 0x40130410>, <sortwrapper
object at 0x401303c0>, 0, 1]
[6571 refs]

[rhettinger]

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The second was easy to fix.

The first is defying my attempts to fix it. You're welcome
to take a crack at it.

[mwhudson]

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I have a feeling that your fix for problem #2 has made
problem #1 harder to fix...

will have a look later, no time right now.

[mwhudson]

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Here's a much less devious test case:

$ cat w.py
def k(x):
    del l[:]
    return x
 
l = range(10)
l.sort(key=k)
$ ./python w.py
Segmentation fault

i think doing the "hide ob_item" swizzle should be just
about the first thing list_sort does and undoing it should
be about the last. Patch soon (I hope).

[mwhudson]

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Boy is this stuff hard to get right!

See what you think of the attached patch.

[rhettinger]

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On the code path leading to a dsu_fail, does PyMem_FREE()
ever get called?

Would there be some added protection value to INCREFing self
at the beginning and DECREFing it at the end?

[mwhudson]

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On the code path leading to a dsu_fail, does
PyMem_FREE() ever get called?

Good catch. New patch attached.

Would there be some added protection value to INCREFing self
at the beginning and DECREFing it at the end?

Um, I don't think so, as the calling machinery holds a
reference to self (and all the other arguments) during the
call. Or did you mean something else?

[rhettinger]

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Looks good.
Please add your crashers to the test suite and check it all in.

[mwhudson]

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OK, checked in as:

Objects/listobject.c revision 2.167
Lib/test/test_sort.py revision 1.9