DictProxy? What is this?

[Maric Michaud]

Le lundi 26 juin 2006 16:06, digitalorganics at gmail.com a écrit :
> Fredrik Lundh wrote:
> > digitalorganics at gmail.com wrote:
> > > When I tried to update a class's __dict__, I got an error saying that
> > > there is no 'update' attribute for dictproxy object. What is a
> > > dictproxy object?
> >
> > a CPython implementation detail, used to protect an internal data
> > structure used by new-style objects from unexpected modifications.
> >
> > </F>
>
> Ah, so I'm not suppose to be able to change a class's __dict__? Thanks
> Fredrik.

Of course, yes :

In [1]: class a(object) : pass
   ...:

In [2]: a.__dict__
Out[2]: <dictproxy object at 0xa7e01d34>

In [3]: a.__dict__.items()
Out[3]:
[('__dict__', <attribute '__dict__' of 'a' objects>),
 ('__module__', '__main__'),
 ('__weakref__', <attribute '__weakref__' of 'a' objects>),
 ('__doc__', None)]

In [4]: a.__dict__['foo'] = lambda s : True
---------------------------------------------------------------------------
exceptions.TypeError...

TypeError: object does not support item assignment

hmmm, not this way, but :

In [5]: a.foo = lambda s : True

In [6]: a.__dict__.items()
Out[6]:
[('__dict__', <attribute '__dict__' of 'a' objects>),
 ('__module__', '__main__'),
 ('foo', <function <lambda> at 0xa79528ec>),
 ('__weakref__', <attribute '__weakref__' of 'a' objects>),
 ('__doc__', None)]

In [7]: a().foo()
Out[7]: True

or :

In [9]: setattr(a, 'bar', lambda s : False)

In [10]: a().bar()
Out[10]: False


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Maric Michaud
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