Bob B. wrote:
> I've been playing with descriptors lately. I'm having one problem I
> can't seem to find the answer to. I want to assign a descriptor to a
> list of attributes. I know I should be able to add these somewhere in
> the class's __dict__, but I can't figure out where. Here's some code:
>
> class MyDesc(object):
> def __init__(self, name=None, initVal=None):
> self.name = name
> self.value = initVal
>
> def __get__(self, obj, objtype):
> // Do some stuff
> self.value = "blah"
> return self.value
>
> class MyClass(object):
> attributes = ('attr1', 'attr2')
> for attr in attributes:
> exec ("%s=MyDesc('%s')") % (attr, attr)
>
> // More stuff in the class
>
> Ok, that "exec" is an ugly hack. There's gotta be someway to plop
> this straight into the class's __dict__ without doing that, but when I
> try adding self.__class__.__dict__[attr] = MyDesc(attr) in MyClass's
> __init__ method, I get the error: "TypeError: 'dictproxy' object does
> not support item assignment"
Probably the simplest thing is to just add the attributes after the
class body, e.g.::
>>> class MyClass(object):
... pass
...
>>> for attr in ['attr1', 'attr2']:
... setattr(MyClass, attr, MyDesc(attr))
...
>>> c = MyClass()
>>> c.attr1
'blah'
Another option would be to use a metaclass to set the class attributes
at class creation time::
>>> class Meta(type):
... def __init__(cls, name, bases, bodydict):
... for attr in cls._desc_attrs:
... setattr(cls, attr, MyDesc(attr))
...
>>> class MyClass(object):
... __metaclass__ = Meta
... _desc_attrs = ['attr1', 'attr2']
...
>>> c = MyClass()
>>> c.attr1
'blah'
HTH,
STeVe
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