[ python-Patches-1692335 ] Move initial args assignment to BaseException.__new__

Patches item #1692335, was opened at 2007-04-01 13:46
Message generated for change (Comment added) made by gbrandl
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1692335&group_id=5470

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Core (C code)
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Ziga Seilnacht (zseil)
Assigned to: Nobody/Anonymous (nobody)
Summary: Move initial args assignment to BaseException.__new__

Initial Comment:
Pickling exceptions fails when an Exception class
requires an argument in the constructor, but doesn't
call its base class' constructor.  See this mail
for details:

http://mail.python.org/pipermail/python-dev/2007-April/072416.html

This patch simply moves initial args assignment to
BaseException.__new__. This should fix most of the
problems, because it is very unlikely that an
exception overwrites the __new__ method; exceptions
used to be old style classes, which don't support
the __new__ special method.

The args attribute is still overwritten in all the
__init__ methods, so there shouldn't be any backward
compatibility problems.



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

>Comment By: Georg Brandl (gbrandl)
Date: 2007-08-11 09:06

Message:
Logged In: YES 
user_id=849994
Originator: NO

Attaching a new patch that fixes the 

class D(Exception):
    def __init__(self, foo):
        self.foo = foo
        Exception.__init__(self)

scenario by keeping the original args to __new__ as an exception
attribute.
File Added: exception-pickling.diff

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

Comment By: Eric Huss (ehuss)
Date: 2007-06-27 18:45

Message:
Logged In: YES 
user_id=393416
Originator: NO

Added patch #1744398 as an alternate solution.


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

Comment By: Eric Huss (ehuss)
Date: 2007-06-15 00:34

Message:
Logged In: YES 
user_id=393416
Originator: NO

I have stumbled across another scenario where unpickling fails.  If your
exception takes arguments, but you call Exception.__init__ with a different
number of arguments, it will fail.  As in:

class D(Exception):
    def __init__(self, foo):
        self.foo = foo
        Exception.__init__(self)


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

Comment By: Ziga Seilnacht (zseil)
Date: 2007-04-01 21:50

Message:
Logged In: YES 
user_id=1326842
Originator: YES

I'm attaching a test that Eric Huss sent in private
mail.

The test fails, because old exception pickles don't
have args for the reconstructor, but their __init__()
gets called anyway because they are new style classes
now.

The problem is in cPickle.InstanceNew() and
pickle.Unpickler._instantiate().  Those methods behave
differently depending on the type of the object
instantiated; they avoid the __init__() call when type
is an old style class.

There is nothing that can be done in the exception
classes to fix this issue; the fix would need to be
in the pickle and cPickle module.
File Added: test_exception_pickle.py

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

Comment By: Ziga Seilnacht (zseil)
Date: 2007-04-01 13:47

Message:
Logged In: YES 
user_id=1326842
Originator: YES

File Added: exc_args_25.diff

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

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1692335&group_id=5470