Can I reference 1 instance of an object by more names ? rephrase

[stef]

Bruno Desthuilliers wrote:
> stef a écrit :
>> thanks Guys for your information,
>>
>> indeed you're all quit right,
>> but I think I've not correctly described my problem :-(
>>
>> I need to have 2 (or more) names, that references the same instance 
>> of an object,
>> and in assigning a value to the object (or to some property in the 
>> object),
>> I need to do extra activities (like changing some global variables).
>
> Then you want a property (aka computed attribute).
>
>> Now if I use  a "container type object", without actual using the 
>> index of the container object,
>> I get things working OK.
>> But now I have to use a dummy index, if I use the object in 
>> assignments, see program below.
>> Is there another way, without using the dummy index, to achieve the 
>> same results ?
>
>> thanks,
>> Stef Mientki
>>
>> <Python>
>> class cpu_ports(object):
>>    def __init__(self, value=0):
>>        self._d = value
>>    def __setitem__(self, index, value):
>>      print 'vv'
>>      self._d = value
>>    def __getitem__(self, index):
>>      return self._d
>>    def __repr__(self):
>>      return str(self._d)
>>
>> name1 = cpu_ports()     # create an instance
>> name2 = name1            # refer with a second name to the same instance
>> print name1, name2      # test ok
>>
>> name1[0] = 25               # assign a value to the instance
>> print name1, name2      # both references are OK
>>
>> name2[0] = 26               # assign another value through the other 
>> name
>> print name1, name2      # both reference are OK
>>
>> name2[0] = name1[0] + 13  # use both names at either side of an 
>> assignment
>> print name1, name2            # both references still OK
>
> You can have something working the same way using a property, but 
> that's how far you'll get - if you hoped to be able to automagically 
> rebind name2 when rebinding name1, then too bad, because python wont 
> let you do so. You have to understand that
>   name = obj
> is totally different from
>   name.attr = obj
> or
>   name[index] = obj
>
> In the first case, this is *really* a binding, and that's one of the 
> few things that Python won't let you mess with. In the two last cases, 
> it's in fact a method call - as the use of __[get|set]item__ should 
> make obvious.
>
> here's an example using a property:
>
> class cpu_ports(object):
>    def __init__(self, value=0):
>        self._d = value
>    @apply
>    def value():
>        def fset(self, value):
>            print 'vv'
>            self._d = value
>        def fget(self):
>            return self._d
>        return property(**locals())
>
>    def __repr__(self):
>        return str(self._d)
>
> name1 = cpu_ports()     # create an instance
> name2 = name1            # refer with a second name to the same instance
> print name1, name2      # test ok
>
> name1.value = 25               # assign a value to the instance
> print name1, name2      # both references are OK
>
> name2.value = 26    # assign another value through the other name
> print name1, name2      # both reference are OK
>
> name2.value = name1.value + 13
> print name1, name2      # both reference are OK
>
> And that's about as far as you can go (without rewriting Python I mean).
thanks Bruno for your clear explanation,
I was "afraid" that this would be the only solution,
and now I'm sure,
I can implement it in this way (which is not really a problem).

I just found a Python compiler for PICs (Pyastra),
I still have to study it, but it might be a good idea,
to translate JAL to Python, using the exact syntax of Pyastra.

thanks again,
Stef Mientki