Alex Martelli napisał(a):
>> Can you also check my reasoning for getting attributes?
>>
>> value = obj.attr
>> * if instance class has __getattribute__, call it
>> * else: lookup "attr" in all parent classes using class __mro__;
>> if it's a descriptor call its __get__ method, return its value
>> otherwise (when descriptor doesn't have __get__, it's unreadable
>> and AttributeError is raised)
>> * else: check instance __dict__ for "attr", return it when found
>> * else: lookup __getattr__ in instance class and call it when found
>> * else: raise AttributeError
>
> No, the value found in the instance (your second 'else' here) takes
> precedence if the descriptor found in the first 'else' is
> non-overriding.
Oh, right. My mistake comes from the subtle difference between defining
descriptor as a class and by property() builtin (I've tested only second
option and assumed that descriptor without __set__ cannot be rebinded):
class non_overriding(object):
def __get__(*a):
return 12
class C(object):
x = non_overriding()
y = property(lambda s:23)
c = C()
c.x = 4
print c.x # => 4
c.y = 5 # => AttributeError: can't set attribute
IMHO that's not very consistent. Well, probably some code rely on this,
so I just have to live with it.
Thanks for your time and patience in explaining my doubts.
mk
--
. o . >> http://joker.linuxstuff.pl <<
. . o It's easier to get forgiveness for being wrong
o o o than forgiveness for being right.
--
http://mail.python.org/mailman/listinfo/python-list
