Scope rule pecularities

[Antoon Pardon]

Op 2004-05-12, Donn Cave schreef <donn at u.washington.edu>:
> In article <slrnca4693.1i9.apardon at trout.vub.ac.be>,
>  Antoon Pardon <apardon at forel.vub.ac.be> wrote:
>
>> Op 2004-05-12, Duncan Booth schreef <me at privacy.net>:
>> > Antoon Pardon <apardon at forel.vub.ac.be> wrote in 
>> > news:slrnca428q.1i9.apardon at trout.vub.ac.be:
>> >
>> >> IMO lacking an assignment that copies the value
>> >> of one object into another was a mistake and
>> >> which creats IMO a lot of difficulties.
>> >> 
>> >> If I have a function with an object as a paramter.
>> >> and this object is mutable. Now within this function
>> >> I find a second object with the value I want the
>> >> argument to have. Now I can't simply copy the
>> >> second object over the argument but I have to
>> >> copy attribute by attribute from the second object
>> >> into the argument.
>> >
>> > Why wouldn't you just return the second value (or a copy of it) as a result 
>> > from the function? That is usually a more flexible choice since it gives 
>> > the caller the option of either replacing the original value or using the 
>> > modified value somewhere different.
>> 
>> Well because the object could be bound with more than one name.
>> 
>> > Anyway, if you really need to do this then the mutable object should have 
>> > some sort of updateState method which takes the second object as a 
>> > parameter. That way the original object can have control over which 
>> > attributes get overwritten and which don't.
>> 
>> And I think it is a pain in the butt to always have to write such an
>> UpdateState method whenever you want one object to be copied in place
>> from an other.
>
> I really think this is a cases where you will write better
> programs if you let yourself be guided by what you can do
> in idiomatic Python.

I don't know. My attitude is that I don't program in a language.
I program by outlining structurers, functionality, algorithm,
etc which are then translated
into a language. I judge languages by how much I have to fight
them in getting this translation. Of course the knowledge of
languages has an influence in how I outline these things,
but I don't do the outline with a particular language in
mind.

> In modern programming, now that we have pretty much adopted
> the "structured" programming model, one of the main remaining
> burdens on the programmer is "mutable state".   You need to
> be able to account for possible changes in values, if you
> want to be able to reason about your program.  Python isn't
> any kind of extreme solution to this problem, it isn't a
> "pure" functional language, but it does have some helpful
> constraints and this is one of them - you know a function
> can't rebind names that you supply as its parameters.  The
> inability to do this is a feature.

But I don't ask for rebinding, I ask for easy in place copying.

Lets name a new operator "@=" Now given variables A and C
of the same class I would like to see the following:

>>> B = A
>>> A @= C
>>> A is B
True
>>> A is C
False
>>> A == C
True

And maybe if D is of an other class

>>> D @= C
TypError

-- 
Antoon Pardon