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

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Patches item #1692335, was opened at 2007-04-01 06:46
Message generated for change (Comment added) made by ehuss
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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.



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Comment By: Eric Huss (ehuss)
Date: 2007-06-14 17:34

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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)


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Comment By: Ziga Seilnacht (zseil)
Date: 2007-04-01 14:50

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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

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Comment By: Ziga Seilnacht (zseil)
Date: 2007-04-01 06:47

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File Added: exc_args_25.diff

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