[Python-Dev] Making types behave like classes

[Gordon McMillan]

[Gordon]
> > I think it would probably enhance confusion to have the "look
> > more like" without "being more like".
[Paul] 
> Looking more like is the same as being more like. In other words,
> there are a finite list of differences in behavior between types
> and classes and I think we should chip away at them one by one
> with each release of Python.

There's only one difference that matters: subclassing. I don't 
think there's an incremental path to that that leaves Python 
"easily extended".

[Gordon]
> > __class__ is a callable object. It has a __name__. From the
> > Python side, a type isn't much more than an address. 
> 
> Type objects also have names. 

But not a __name__.

> They are not (yet) callable but I
> cannot think of a circumstance in which that would matter. 

Take a look at copy.py.

> Anyhow, I think that type objects should be callable just like
> classes...but I'm trying to pick off low-hanging fruit first. I
> think that the less "superficial" differences there are between
> types and classes, the easier it becomes to tackle the deep
> differences because more code out there will be naturally
> polymorphic instead of using: 
> 
> if type(obj) is InstanceType: 
>  do_onething() 
> else: 
>  do_anotherthing()
> 
> That is an evil pattern if we are going to merge types and
> classes.

And it would likely become:
 if callable(obj.__class__):
   ....

Explicit is better than implicit for warts, too.
 


- Gordon