py3k feature proposal: field auto-assignment in constructors

[Steven D'Aprano]

On Sun, 27 Jan 2008 19:13:27 -0500, Terry Reedy wrote:

[snip]

> class Test(object):
>      @autoassign
>      def __init__(self, _foo, _bar, baz):
>          print 'baz =', baz

[snip]

> I think this version, with this name convention, is nice enough to
> possibly go in the stdlib if there were an appropriate place for it. 
> Not sure where though.  If there were a classtools module....

-1/2

I don't like the name convention. _name already has a perfectly good 
convention: it's a private name, don't mess with it. That includes in 
function/method signatures. With your convention, _foo is public.

I suppose you could write __foo for a private name, and ___foo for a 
*really* private name, relying on the decorator to strip one of the 
underscores. But counting all those underscores is a PITA, and what 
happens if you don't actually want that private name set as an instance 
attribute?

As nice as this feature would be, and I vote +2 on the functionality, I 
wonder whether the amount of line noise in method definitions now will be 
approaching Perlish levels? We've got default values, type annotations 
(in Python3), *args and **kwargs, _ private names, and now we want to add 
auto-assignment.

If we do get syntax support, I vote +1 on &foo, +1/2 on @foo, -1 on .foo 
and -1 on self.foo. (It's explicit, but it's long...).


-- 
Steven