variable variables

[Jean-Michel Pichavant]

someone wrote:
> On Jun 18, 12:49 pm, James Mills <prolo... at shortcircuit.net.au> wrote:
>   
>> On Fri, Jun 18, 2010 at 8:31 PM, someone <petshm... at googlemail.com> wrote:
>>     
>>> I was looking for a "short way" to do it because I have a lot
>>> "some_object.attr.attr or some_object.other_attr.attr" in code. it
>>> looks like I cannot replace attr with just other variable and must
>>> type some_object.other_attr.attr or your solution which is however
>>> longer to type :)
>>>       
>> It would actually help to see some code.
>>
>>     
>
> here it is, In Foo I'd like to have instead of A self.type and the
> same in class B
>
> from some_module import some_object
>
> class Foo:
>     def __init__(self):
>         self.type = 'A'
>
>     def printAttr(self):
>         some_object.A.B
>         some_object.A.C
>         some_object.A.D
>         some_object.A.E
>         some_object.A.F
>         some_object.A.G
>
> class Bar:
>     def __init__(self):
>         self.type = 'B'
>
>     def printAttr(self):
>         some_object.B.B
>         some_object.B.C
>         some_object.B.D
>         some_object.B.E
>         some_object.B.F
>         some_object.B.G
>
>   
>> --James
>>     
>
>   

Here is a way to to do it. Note that it is quite dangereous 'cause you 
may confuse everyone by accessing some_object attributes like a Foo 
attributes. Basically, when the attributes is not found in the Foo 
namespace, it will use the some_object.A or some_object.B namespace instead.


some_object = Bar()
some_object.A = Bar()
some_object.B = Bar()
some_object.A.bar = 'I come from A'
some_object.B.bar = 'I come from B'

class Foo(object):

    def __init__(self, _type):
       self.type = _type

    def __getattribute__(self, name):
       try:
           return object.__getattribute__(self, name)
       except AttributeError:
           return getattr(getattr(some_object, self.type), name)

    def __setattr__(self, name, value):
        try:
            # first look if self has the attribute, if so set it
            if object.__getattribute__(self, name):
                return object.__setattr__(self, name, value)
        except AttributeError:
            # look into some_object
            try:
                _type = object.__getattribute__(self, 'type')
                if hasattr(getattr(some_object, _type), name):
                    return setattr(getattr(some_object, _type), name, value)
            except AttributeError:
                pass
        # attribute neither found in self nor in some_object, let's 
create it in self
        return object.__setattr__(self, name, value)

fa = Foo('A')
fb = Foo('B')

print fa.bar
 > I come from A

print fb.bar
 > I come from B

fa.bar = 'hello world'

print some_object.A.bar
 > hello world



JM