[Python-ideas] Support other dict types for type.__dict__

[Ronny Pfannschmidt]

On 02/24/2012 01:27 AM, Victor Stinner wrote:
>> And you can't use __slots__ because...?
>
> Hum, here is an example:
> ---
note untested, since written in mail client:

class Enum(object):
   __slots__ = ("_data",)
   _data = WriteOnceDescr('_data') # left as exercise

   def __init__(self, **kw):
     self._data = frozendict(kw)

   def __getattr__(self, key):
     try:
        return self._data[key]
     except KeyError:
        raise AttributeError(key)





> def Enum(**kw):
>     class _Enum(object):
>         __slots__ = list(kw.keys())
>         def __new__(cls, **kw):
>             inst = object.__new__(cls)
>             for key, value in kw.items():
>                 setattr(inst, key, value)
>             return inst
>     return _Enum(**kw)
>
> components = Enum(red=0, green=1, blue=2)
> print(components.red)
> components.red=2
> print(components.red)
> components.unknown=10
> ---
>
> components.unknown=10 raises an error, but not components.red=2.
> __slots__ denies to add new attributes, but not to modify existing
> attributes.
>
> The idea of using a frozendict is to deny the modification of an
> attribute value after the creation of the object. I don't see how to
> use __slots__ to implement such constraints.
>
> Victor
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