[ python-Bugs-651701 ] Bozo getstate w/ slots overrides base

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Bugs item #651701, was opened at 2002-12-10 23:10
Message generated for change (Comment added) made by astraw
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Category: Type/class unification
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Peter Fein (pafein)
Assigned to: Nobody/Anonymous (nobody)
Summary: Bozo getstate w/ slots overrides base

Initial Comment:
The bozo __getstate__ set automatically on classes
defining __slots__ overrides any __getstate__ defined
in a base class.  This makes writing a mixin to
implement this method impossible.

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Comment By: Andrew Straw (astraw)
Date: 2003-11-24 05:28

Message:
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I'm experiencing this behavior on Python 2.2.2 and 2.2.3.  I don't 
get it on 2.2(.0) or 2.3(.x).  

Here's a script that demonstrates:  (Sorry SF doesn't seem to 
have a nice attachment feature for comments.)
import sys

print 'Python version',sys.version
print

def recursive_base_class_finder(klass):
    """A function to find all base classes."""
    result = [klass]
    for base_class in klass.__bases__:
        for base_base_class in 
recursive_base_class_finder(base_class):
            result.append(base_base_class)
    # Make only a single copy of each class found
    result2 = []
    for r in result:
        if r not in result2:
            result2.append(r)
    return result2

class A(object):
    __slots__ = ['a']
    def __getstate__(self):
        """support for being pickled"""
        result = {}
        classes = recursive_base_class_finder(self.__class__)
        for klass in classes:
            if hasattr(klass,'__slots__'):
                for attr in klass.__slots__:
                    if hasattr(self,attr):
                        result[attr] = getattr(self,attr)
        return result

    def __setstate__(self,dict):
        for attr in dict.keys():
            setattr(self,attr,dict[attr])
    def __init__(self):
        self.a='a'
        
class B(A):
    __slots__ = ['b']
    def __init__(self):
        A.__init__(self)
        self.b = 'b'
        
a1=A()
b1=B()

import pickle
ap = pickle.dumps(a1)
bp = pickle.dumps(b1)
    
a2 = pickle.loads(ap)
b2 = pickle.loads(bp)

if a2.a == 'a':
    print 'pickling/unpickling ok'
else:
    print 'WARNING: pickling/unpickling failed'
    
if b2.a == 'a' and b2.b == 'b':
    print 'pickling/unpickling on derived class ok'
else:
    print 'WARNING: pickling/unpickling on dericed class failed'

try:
    a2.xx = 'x'
    failed = 0
except:
    failed = 1

if not failed:
    print "WARNING: assigned to attribute not in __slots__"
    
try:
    b2.xx = 'x'
    failed = 0
except:
    failed = 1

if not failed:
    print "WARNING: assigned to attribute in derived class not in 
__slots__"

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Comment By: Raymond Hettinger (rhettinger)
Date: 2003-07-12 01:36

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Peter, is this still an issue?
Can you attach a script demonstrating the problem?

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Comment By: Neal Norwitz (nnorwitz)
Date: 2003-05-22 22:15

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There was an issue with that, IIRC.  There was a discussion
on python-dev a while ago which Guido talked about the
issues.  I don't remember when or what the issues were. 
Probably about 3-6 months ago.  I think the code in this
area may have changed, so it would be beneficial to test
with 2.3b1.

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Comment By: Peter Fein (pafein)
Date: 2003-05-22 22:09

Message:
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This issue is that although the base class B defines a
__getstate__, the class C2 overrides it b/c it contains 
__slots__.  Basically, I'm suggesting that base classes
should be checked for getstate instead of only looking at
the class that defines slots before adding the bozo'd version.

Unfortunately, I don't have a 2.3* version to play with at
the moment.  Please let me know if this clarifies things.

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Comment By: Neal Norwitz (nnorwitz)
Date: 2003-05-22 21:58

Message:
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What do you expect to be printed?  I'm not sure what you
want changed.  Have you tested with 2.3b1?  Does this meet
your needs?

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