[Python-bugs-list] [ python-Bugs-451773 ] new-style objects not weak-referencable

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Bugs item #451773, was opened at 2001-08-16 15:19
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Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Fred L. Drake, Jr. (fdrake)
Assigned to: Guido van Rossum (gvanrossum)
Summary: new-style objects not weak-referencable

Initial Comment:
Objects using the new-style class types are not weakly referencable:

>>> import weakref
>>> class MyClass(object):
...    pass
...
>>> o = MyClass()
>>> weakref.ref(o)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: 'MyClass' objects are not weakly referencable


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>Comment By: Guido van Rossum (gvanrossum)
Date: 2001-08-17 11:57

Message:
Logged In: YES 
user_id=6380

This is a little tricker than I thought.

I don't want to enable weak-referencing for the 'object'
type, because that would add a weak reference slot to every
type (even list, dictionary etc.).

So I have to add a weakref slot at the same time that I add
the __dict__.  But then types using __slots__ are not
weak-referenceable.

Ideally, weak-referenceability might be a user option,
default on for types with a __dict__ but default of for
types that use __slots__ only.

Fred, would it be a safety issue if the list of weak
references were made available as a __weakrefs__ special
slot (if present)?

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