Python. Define "attribute initial method"

Question

I have:

class C:
    aaa=2


class B:
     def __init__ (self,name):
         self.name
         self.value

How can i define class C so when i dynamically set attribute to instance it make that attribute instance of class B. And attribute name of class B have to have attribute name equal string of name of that new attribute in class C and attribute value of B instance have to have value what set in new attribute in instance of class C.

Have to give me that result:

>> c=C()
>> c.whatever= 'strinstrinsstring'
>> isinstance(c.whatever,B)
True
>> c.whatever.value
'strinstrinsstring'
>>c.whatever.name
'whatever'

Answer 1

Just smartly override __setattr__. If you want to do it only for a specific attribute, then put in a special case for the attribute name that you want to look for:

>>> class B:
    def __init__(self, name, value):
        self.name = name
        self.value = value


>>> class C:
    def __setattr__(self, name, value):
        if name == 'makeMeB':
            newb = B(name, value)
            self.__dict__[name] = newb
        else:
            self.__dict__[name] = value

>>> c = C()
>>> c.makeMeB = 'foo'
>>> isinstance(c.makeMeB, B)
True
>>> c.makeMeB.name
'makeMeB'
>>> c.makeMeB.value
'foo'
>>> c.blah = 'foo'
>>> isinstance(c.blah, B)
False

If you want it for every attribute, just forget the if and it'll do it for everything:

>>> class B:
    def __init__(self, name, value):
        self.name = name
        self.value = value


>>> class C:
    def __setattr__(self, name, value):
        attr_as_b = B(name, value)
        self.__dict__[name] = attr_as_b

>>> c = C()
>>> c.makeMeB = 'foo'
>>> isinstance(c.makeMeB, B)
True
>>> c.makeMeB.name
'makeMeB'
>>> c.makeMeB.value
'foo'
>>> c.amIalsoB = 'well?'
>>> isinstance(c.amIalsoB, B)
True
>>> c.amIalsoB.name
'amIalsoB'
>>> c.amIalsoB.value
'well?'

Answer 2

This is a horrible thing to do, because it changes what attributes mean!

Why not just look at the __dict__ of c:

>>> class C(object):
...     pass
...
>>> c = C()
>>> c.spam = 'ham'
>>> c.__dict__
{'spam': 'ham'}