Proposal: reducing self.x=x; self.y=y; self.z=z boilerplate code

[Andrew Koenig]

"Ralf W. Grosse-Kunstleve" <rwgk at yahoo.com> wrote in message 
news:mailman.1236.1120298654.10512.python-list at python.org...

>    class grouping:
>
>        def __init__(self, .x, .y, .z):
>            # real code right here

> Emulation using existing syntax::

>        def __init__(self, x, y, z):
>            self.x = x
>            del x
>            self.y = y
>            del y
>            self.z = z
>            del z

I think this is a bad idea, for a subtle reason.

In Python, unlike many other languages, the names of formal parameters are 
part of a function's interface. For example:

    def f(x, y):
        return x-y

Now f(3, 4) is -1 and f(y=3,x=4) is 1.

The names of instance variables are generally not part of a class' 
interface--they are part of its implementation.

This proposed feature, whenever used, would tie a class' implementation to 
the interface of every method that uses the feature.  As far as I can see, 
it is impossible to use the feature without constraining the implementation 
in this way.

For this reason, I would much rather have the mapping between parameter 
names and instance variables be explicit.