En Thu, 19 Feb 2009 01:29:17 -0200, Alan G Isaac <[email protected]>
escribió:
OK, that's good. I'd like to sometimes lock attribute creation on
instances of a class but still allow properties to function
correctly. Will something like below be satisfactory?
def __setattr__(self, attr, val):
"""If instance locked, allow no new attributes."""
try:
#get the class attribute if it exists
p = getattr(type(self),attr)
#if it's a descriptor, use it to set val
p.__set__(self, val)
except AttributeError: #no descriptor
if hasattr(self, attr): #update val
self.__dict__[attr] = val
elif getattr(self, '_attrlock', False):
raise AttributeError(
"Set _attrlock to False to add attributes.")
else:
#new attributes allowed
self.__dict__[attr] = val
The problem with using __setattr__ is that is slows down *all* attribute
writes considerably.
In particular, your code prevents using class attributes as a default
value for instance attributes (not a big deal, but I like it sometimes),
and you must remember to set a value for all attributes (even the "hidden"
ones used by any property). But if you feel OK with that, "just do it". I
think there are a few recipes in the Python Cookbook about this topic too.
--
Gabriel Genellina
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