[Python-bugs-list] [ python-Bugs-502085 ] pickle problems (with Boost.Python)

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Bugs item #502085, was opened at 2002-01-10 14:49
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=502085&group_id=5470

Category: Python Library
Group: Python 2.2
Status: Open
Resolution: None
Priority: 5
Submitted By: Ralf W. Grosse-Kunstleve (rwgk)
Assigned to: Nobody/Anonymous (nobody)
Summary: pickle problems (with Boost.Python)

Initial Comment:
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


----------------------------------------------------------------------

>Comment By: Guido van Rossum (gvanrossum)
Date: 2002-01-11 10:39

Message:
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.


----------------------------------------------------------------------

Comment By: Ralf W. Grosse-Kunstleve (rwgk)
Date: 2002-01-11 09:17

Message:
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

----------------------------------------------------------------------

Comment By: Guido van Rossum (gvanrossum)
Date: 2002-01-10 21:07

Message:
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.

----------------------------------------------------------------------

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