pickle problems (with Boost.Python)

@mwhudson

BPO	502085
Nosy	@mwhudson, @gvanrossum, @tim-one

^{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/gvanrossum'
closed_at = <Date 2011-03-16.17:48:13.762>
created_at = <Date 2002-01-10.22:49:22.000>
labels = ['library']
title = 'pickle problems (with Boost.Python)'
updated_at = <Date 2011-03-16.17:48:13.762>
user = 'https://bugs.python.org/rwgk'

bugs.python.org fields:

activity = <Date 2011-03-16.17:48:13.762>
actor = 'brett.cannon'
assignee = 'gvanrossum'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2002-01-10.22:49:22.000>
creator = 'rwgk'
dependencies = []
files = []
hgrepos = []
issue_num = 502085
keywords = ['patch']
message_count = 8.0
messages = ['8702', '8703', '8704', '8705', '8706', '8707', '8708', '8709']
nosy_count = 5.0
nosy_names = ['mwh', 'gvanrossum', 'tim.peters', 'rwgk', 'brandon-rhodes']
pr_nums = []
priority = 'high'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue502085'
versions = ['Python 2.2']

Boost.Python
(http://www.boost.org/libs/python/doc/index.html) is a
popular package for integrating Python and C++.

Boost.Python pickle support is broken when using
Python 2.2 final, but
works with Python 2.2c1.

I noticed this difference:

diff /usr/local_cci/Python-
2.2/lib/python2.2/pickle.py /usr/local_cci/Python-
2.2c1/lib/python2.2/pickle.py
26c26
< __version__ = "$Revision: 1.56 $" # Code
version
---

__version__ = "$Revision: 1.55 $" # Code
version
166,169d165
< if issubclass(t, TypeType):
< self.save_global(object)
< return

I inserted one line in pickle.py:

% diff /usr/local_cci/Python-
2.2/lib/python2.2/pickle.py .
165a166

        print "t", t

Result:

t <extension class pickle1.world at 1400c9c08>
t 
<boost::python::meta_class<boost::python::detail::exten
sion_instance> object at 0x3ffffe41ae0>
Traceback (most recent call last):
  File "zi", line 9, in ?
    pstr = pickle.dumps(wd)
  File "pickle.py", line 974, in dumps
    Pickler(file, bin).dump(object)
  File "pickle.py", line 115, in dump
    self.save(object)
  File "pickle.py", line 216, in save
    self.save_reduce(callable, arg_tup, state)
  File "pickle.py", line 241, in save_reduce
    save(callable)
  File "pickle.py", line 167, in save
    if issubclass(t, TypeType):
TypeError: issubclass() arg 1 must be a class

The following patch restores backward-compatibility:

% diff /usr/local_cci/Python-
2.2/lib/python2.2/pickle.py .
166,168c166,173
< if issubclass(t, TypeType):
< self.save_global(object)
< return
---

        try:
            issc = issubclass(t, TypeType)
        except TypeError:
            pass
        else:
            if issc:
                self.save_global(object)
                return

Remark: I also noticed that 2.2 cPickle still works
for us
(double-checked) even though the CVS logs indicate
that it was
also modified between 2.2c1 and 2.2.

Thanks,
Ralf

Logged In: YES
user_id=6380

Hm, I'm surprised that t (which was returned by
type(object)) is not considered a type. Can you explain the
Boost metaclass hierarchy a bit so that I can understand how
this can work? It was found in the ob_type slot of the
object (because that's what type() returns) so it should
look a lot like a type! Then why isn't it one?

IOW I think that the correct solution would be a change to
Boost. But I'm open to persuasion.

Logged In: YES
user_id=71407

IOW I think that the correct solution would be a change to
Boost. But I'm open to persuasion.

In principle I agree with you, but here are a few arguments
to
justify the easy fix:

The old Boost.Python metaclass system is a dead branch.
We would prefer to concentrate our time on the ongoing
rewrite of Boost.Python which will be fully based on
the new Python 2.2 type system.
A significant number of people are using released versions
of Boost(.Python). If the easy fix is integrated in
Python 2.2.1,
they could continue to use what they have.
Other people might be affected by your change. The
suggested solution
will restore backward-compatibility with more people's
existing code.
This is more a question: can you envision that the
suggested
fix has negative side-effects?

Thanks,
Ralf

Logged In: YES
user_id=6380

Ah, I didn't realize this was the old Boost. I should have
(the new one only runs on Python 2.2).

I'll think about it.

Logged In: YES
user_id=71407

python 2.2.1c1 still exhibits the problem described
in the original posting. Is this expected? Is there
still hope that the suggested fix/work-around is
considered for 2.2.1?
Thanks,
Ralf

Logged In: YES
user_id=31435

Boosted priority and assigned to Guido. Guido, if you want
to do something here for 2.2.1, now's the time.

Logged In: YES
user_id=6380

I checked in a fix on the trunk.

There's nothing I can do to get this into 2.2.1c2, but
Michael might be willing to put it in 2.2.1final. Otherwise
it should go into 2.2.2, if we ever release one.

(Sorry -- I forgot about this, and you were just a tad too
late to make the 2.2.1c2 release.)

Logged In: YES
user_id=6656

It's in 221c2

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pickle problems (with Boost.Python) #35903

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pickle problems (with Boost.Python) #35903

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rwgk commented on Jan 10, 2002

gvanrossum commented on Jan 11, 2002

rwgk commented on Jan 11, 2002

gvanrossum commented on Jan 11, 2002

rwgk commented on Mar 25, 2002

tim-one commented on Mar 25, 2002

gvanrossum commented on Mar 26, 2002

mwhudson commented on Mar 26, 2002

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