[ python-Bugs-1448042 ] Defining a class with __dict__ brakes attributes assignment

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Bugs item #1448042, was opened at 2006-03-11 17:49
Message generated for change (Comment added) made by tjreedy
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Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Michal Kwiatkowski (rubyjoker)
Assigned to: Nobody/Anonymous (nobody)
Summary: Defining a class with __dict__ brakes attributes assignment

Initial Comment:
When defining a class with __dict__ attribute, its 
instances can't rebind their __dict__ attributes.

--------------------------------------------------

class C(object): __dict__ = {}

obj = C()
obj.a = object()

import gc
gc.get_referrers(obj.a) # => [{'a': <object object at 
0x811d5b0>}]

obj.__dict__ = {} # doesn't really bind new __dict__

vars(obj) # => {}
object.__getattribute__(obj, '__dict__') # => {}
object.__getattribute__(C, '__dict__') # => {..., but 
without "a"}
obj.a  # => <object object at 0x811d5b0> (no exception
!)

gc.get_referrers(obj.a) # => [{'a': <object object at 
0x811d5b0>, '__dict__': {}}]

--------------------------------------------------

Although neither class nor object has an attribute "a", 
it's still accessible. It's also not possible to rebind 
__dict__ in that object, as it gets inside real object 
attributes dictionary.

This behaviour has been tested on Python 2.2, 2.3 and 
2.4, but may as well affect earlier versions.

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>Comment By: Terry J. Reedy (tjreedy)
Date: 2006-03-17 22:21

Message:
Logged In: YES 
user_id=593130

To me, this falls under the category of 'don't do that'.

http://docs.python.org/ref/id-classes.html
2.3.2 Reserved classes of identifiers 
__*__ 
System-defined names. These names are defined by the 
interpreter and its implementation ...

To me, this means to use them in the manner specified or 
you get what you get. 

http://docs.python.org/ref/types.html#l2h-120
defines the internal usage of '__dict__'.  There is, as 
far as I know, no specified usage for rebinding '__dict__'.

So unless someone has a better idea that won't slow down 
proper usage, I would close this as 'invalid' or 'wont 
fix'.

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