copy.copy corrupts objects that return false value from __getstate__

[alga]

BPO	7848
Nosy	@avassalotti
Superseder	bpo-6827: deepcopy erroneously doesn't call setstate if getstate returns empty dict

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2010-02-07.09:33:11.212>
created_at = <Date 2010-02-03.18:18:43.508>
labels = ['type-bug', 'library']
title = 'copy.copy corrupts objects that return false value from __getstate__'
updated_at = <Date 2010-02-07.09:33:11.212>
user = 'https://bugs.python.org/alga'

bugs.python.org fields:

activity = <Date 2010-02-07.09:33:11.212>
actor = 'georg.brandl'
assignee = 'none'
closed = True
closed_date = <Date 2010-02-07.09:33:11.212>
closer = 'georg.brandl'
components = ['Library (Lib)']
creation = <Date 2010-02-03.18:18:43.508>
creator = 'alga'
dependencies = []
files = []
hgrepos = []
issue_num = 7848
keywords = []
message_count = 2.0
messages = ['98793', '98822']
nosy_count = 2.0
nosy_names = ['alexandre.vassalotti', 'alga']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '6827'
type = 'behavior'
url = 'https://bugs.python.org/issue7848'
versions = ['Python 2.6', 'Python 2.5', 'Python 3.1']

[alga]

When copy.copy is used on an object whose __getstate__ returns 0, it can produce a corrupt copy of an object:

>>> import copy
>>> class Foo(object):
...     def __init__(self):
...        self.value = 0
...     def __getstate__(self):
...        return self.value
...     def __setstate__(self, v):
...        self.value = v
... 
>>> one = Foo()
>>> two = copy.copy(one)
>>> two.value
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Foo' object has no attribute 'value'

Pickling/unpickling works fine for this object, so this appears to be a bug in copy._reconstruct.

This is not a contrived example, BTrees.Length.Length from ZODB uses such a __getstate__.

[alga]

This bug is a duplicate of bpo-6827, sorry.