did 2.6.3 regress for some uses of the __doc__ property?

[zooko]

BPO	7183
Nosy	@warsaw, @pitrou, @bitdancer, @moriyoshi

^{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 = None
closed_at = <Date 2010-12-14.15:43:18.051>
created_at = <Date 2009-10-21.23:22:36.260>
labels = ['interpreter-core', 'type-bug']
title = 'did 2.6.3 regress for some uses of the __doc__ property?'
updated_at = <Date 2010-12-14.15:43:18.050>
user = 'https://bugs.python.org/zooko'

bugs.python.org fields:

activity = <Date 2010-12-14.15:43:18.050>
actor = 'r.david.murray'
assignee = 'none'
closed = True
closed_date = <Date 2010-12-14.15:43:18.051>
closer = 'r.david.murray'
components = ['Interpreter Core']
creation = <Date 2009-10-21.23:22:36.260>
creator = 'zooko'
dependencies = []
files = []
hgrepos = []
issue_num = 7183
keywords = []
message_count = 12.0
messages = ['94329', '94330', '94333', '94342', '94343', '94344', '94348', '94356', '94360', '94367', '95156', '123956']
nosy_count = 6.0
nosy_names = ['barry', 'zooko', 'pitrou', 'r.david.murray', 'moriyoshi', 'pveloz']
pr_nums = []
priority = 'high'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue7183'
versions = ['Python 2.6', 'Python 2.7']

[zooko]

According to
https://bugs.edge.launchpad.net/ubuntu/+source/boost1.38/+bug/457688 ,
Python 2.6.3 stopped working for something that Python 2.6.2 worked for,
involving Boost.

Andrew Mitchell looked at the Python 2.6.3 release notes, saw
http://bugs.python.org/issue5890 which was fixed by
http://svn.python.org/view/python/branches/release26-
maint/Objects/descrobject.c?r1=71756&r2=72302&pathrev=72302 . Could this
patch be causing this problem?

[warsaw]

I think this is caused by the fix for bug 5890 and isn't a regression.

[warsaw]

Apparently this affects more than just Boost. lifeless (Robert Collins)
tells me that "__doc__ becoming readonly buggered some code of ours in
bzr too, IIRC".

He thinks it was in pure Python (i.e. not extension code). Does anybody
have a pure Python reproducible example?

[warsaw]

Robert indicated later that this probably did /not/ affect Bazaar.

[bitdancer]

I added some tests in test_property in my checkout and the __doc__
property is not, as far as I can tell, set read-only by the bpo-5890 fix.

The error message referenced in the report is:

AttributeError: 'Boost.Python.StaticProperty' object attribute '__doc__'
is read-only

If Boost.Python.StaticProperty is a subclass of Property, which seems
likely, then the 5890 fix could well be triggering this error, since if
a property created with a subclass is given a docstring, the fix creates
a __doc__ attribute in the subclass's dict. If the subclass dict is
read only, the above error would be triggered.

I don't know enough about extension types to know if the property code
should be special casing extension types, but if it should, then IMO
that would qualify 5890 as a regression. Otherwise I don't think it is,
though we could still consider whether making a change to reduce user
pain is worthwhile. (To be worthwhile it would have to be likely to
reach the users before the Boost fix does...apparently Boos has a fix in
their SVN for this problem.)

I'm guessing that this is a problem only with extension types, not with
pure Python code.

[bitdancer]

That should have been 'instance's dict', not the subclass dict.

[warsaw]

Thanks David, that's what I suspect too (that's its a problem with
extension types). Unless we get more information, I'm not inclined to
hold up the 2.6.4 release for this.

[pitrou]

I'm not sure I understand, how do you create a "read-only instance dict"?

[bitdancer]

I'm not sure you do. I have no idea how Boost works, but the fact that
removing a Boost 'read-only' declaration circumvents the problem in at
least some cases argues that Boost is setting _something_ read-only.

[warsaw]

After discussion on python-dev, this will not block 2.6.4

[moriyoshi]

See my comment on issue bpo-5890. I attached a patch to solve the
Boost.Python issue.