New submission from Eric Snow:
In Objects/typeobject.c, reduce_2() makes _PyObject_GetAttrId() calls to pull
some methods for the object in question. This is a problem when the object's
type defines __getattr__() or __getattribute__() and returns something like
None when the attribute is not found:
from copy import deepcopy
class Spam(dict):
def __getattr__(self, name):
# defaults to None
return self.get(name)
deepcopy(Spam(ham=5))
While we could do a check on the result of _PyObject_GetAttrId() to make sure
it is callable, the better solution would be to look up the methods on the
object's type rather than on the object. Doing so falls in line with the
specified pattern for special method lookup [1]. I'm guessing there are a few
other related places in typeobject.c that have the same problem which could be
fixed in the same way.
I'm marking this as a bug rather than a feature since it is a deviation from
the specification for special methods.
[1] http://docs.python.org/dev/reference/datamodel.html#special-method-lookup
----------
components: Interpreter Core
messages: 173066
nosy: eric.snow
priority: normal
severity: normal
stage: needs patch
status: open
title: object.__reduce__()
type: behavior
versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue16251>
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