rzed wrote:
> I'm confused (not for the first time).
>
> I create these classes:
>
> class T(object):
> def __new__(self):
> self.a = 1
>
> class X(T):
> def __init__(self):
> self.a = 4
>
> class Y:
> def __init__(self):
> self.a = 4
>
> class Z(object):
> def __init__(self):
> self.a = 4
>
>
> ... and these instances:
>
> t = T()
> x = X()
> y = Y()
> z = Z()
>
> and I want to examine the 'a' attributes.
>
>>>> print T.a
> 1
>>>> print y.a
> 4
>>>> print z.a
> 4
>
> So far, it's as I expect, but:
>
>>>> print x.a
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> AttributeError: 'NoneType' object has no attribute 'a'
>
>>>> print t.a
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> AttributeError: 'NoneType' object has no attribute 'a'
>
> So what the heck is 'T'? It seems that I can't instantiate it or
> derive from it, so I guess it isn't a proper class. But it's
> something; it has an attribute. What is it? How would it be used
> (or, I guess, how should the __new__() method be used)? Any hints?
>
__new__ should return something. Since there is no return statement,
None is returned.
You might try something like:
class T(object):
def __new__(cls):
cls= object.__new__(cls)
cls.a= 1
return cls
t= T()
print t.a
Colin W.
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