Bob B. a écrit :
> 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"
>
> Any ideas?
Steven already show you the simplest solution. Now if you want something
"cleaner" (or at least more transparent to persons subclassing MyClass -
which may or may not be a concern), you can use metaclasses too:
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"
if obj is None:
return self
return self.value
class MyType(type):
def __init__(cls, name, bases, dic):
attributes = dic.get('attributes', None)
if attributes is not None:
for attrname, initval in attributes.iteritems():
setattr(cls, attrname, MyDesc(attrname, initval))
class MyClass(object):
__metaclass__ = MyType
attributes = dict(attr1="attr1", attr2="attr2")
class MySubclass(MyClass):
# let you override parent's attributes...
attributes = dict(attr1="otherattr1", attr3="a new one")
HTH
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