On Mon, Mar 3, 2008 at 8:00 AM, Greg Kochanski [EMAIL PROTECTED]
wrote:
If we have a hierarchy of classes, and we use
__getstate__/__setstate__, the wrong version
of __setstate__ gets called.
Possibly, this is a documentation problem, but here goes:
No, it's a typo error :)
Take two classes, A and B, where B is the child of A.
Construct a B. Pickle it. Unpickle it, and you find
that the __setstate__ function for A is called with the result
produced by B.__getstate__().
This is wrong.
An example follows:
import pickle as P
class A(object):
def __init__(self, a):
print 'A.__init__'
self.a = a
def __getstate__(self):
print 'A.__getstate'
return self.a
def __setstate__(self, upstate):
print 'A.__setstate', upstate
self.a = upstate
class B(A):
def __init__(self, a, b):
print 'B.__init__'
A.__init__(self, a)
self.b = b
def __getstate__(self):
print 'B.__getstate'
return (A.__getstate__(self), self.b)
def __setstate(self, upstate):
Try actually calling this method '__setstate__' instead.
# This never gets called!
print 'B.__setstate', upstate
A.__setstate__(self, upstate[0])
self.b = upstate[1]
def __repr__(self):
return 'B a=%d b=%d' % (self.a, self.b)
q = B(1,2)
print '---'
r = P.loads(P.dumps(q, 0))
print 'q=', q
print 'r=', r
Now, run it:
$ python foo.py
B.__init__
A.__init__
---
B.__getstate
A.__getstate
A.__setstate (1, 2)
q= B a=1 b=2, h=46912504218064
r= Traceback (most recent call last):
File foo.py, line 44, in module
print 'r=', r
File foo.py, line 37, in __repr__
return 'B a=%d b=%d' % (self.a, self.b)
AttributeError: 'B' object has no attribute 'b'
$
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Thomas Wouters [EMAIL PROTECTED]
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