Diez B. Roggisch wrote:
>> This still seems not quite right to me... Or more likely seems to be
>> missing something still.
>>
>> (But it could be this migraine I've had the last couple of days
>> preventing me from being able to concentrate on things with more than
>> a few levels of complexity.)
>>
>> Playing around with the shell a bit gives the impression that calling
>> a method in a instance gives the following (approximate) result...
>>
>> try:
>> leader.__dict__["set_name"]("John")
>> except:
>> type(leader).__dict__["set_name"].__get__(leader, "John")
>> # which results in...
>> # Person.set_name(leader, "John")
>> except:
>> raise( AttributeError,
>> "%s object has no attribute %s" \
>> % (leader, "set_name") )
>>
>>
>> Of course this wouldn't use the object names directly... I guess I'll
>> need to look in the C object code to see exactly how it works. But
>> the links you gave help.
>
>
> I guess you mean to indent the whole part after the first except and put
> a try beforehand?
Yes, I did. I'm not sure why I left out the try.
try:
leader.__dict__["set_name"]("John")
except:
try:
type(leader).__dict__["set_name"].__get__(leader, "John")
# which results in...
# Person.set_name(leader, "John")
except:
raise( AttributeError,
"%s object has no attribute %s" \
% (leader, "set_name") )
> Apart from that you seem to be right - there can very well be values in
> the class dict that don't follow the descriptor-protocol. However my
> playing around with this stuff indicates that the creation of bound
> methods relies on the method being wrapped in a descriptor - otherwise,
> you get the notorious TypeError
>
> set_name() takes exactly 1 argument (0 given)
>
> as the binding doesn't occur.
>
> Regards,
>
> Diez
What I've noticed is you can block the visibility of a class attribute,
which include methods, by inserting an object in the instance with the
same name.
Python 2.4.1 (#65, Mar 30 2005, 09:13:57) [MSC v.1310 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> class a(object):
... def b(self, value):
... print value
...
>>> aa = a()
>>> def foo(value):
... print "%r" % value
...
>>> aa.b('hello')
hello
>>> aa.b = foo
>>> aa.b('hello')
'hello'
>>> del aa.b
>>> aa.b('hi there')
hi there
>>>
So the underlying mechanism for calling methods doesn't kick in until
*after* an attempt to get an attribute of the same name in the instance.
>>> a.boo = boo
>>> def boo(self, value):
... print list(value)
...
>>> a.boo = boo
>>> aa.boo('hello')
['h', 'e', 'l', 'l', 'o']
The attribute aa.boo is not there, so call boo.__get__() in class a.
Cheers,
Ron
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