[Python-ideas] Composition over Inheritance

Soni L. fakedme+py at gmail.com
Sat Oct 28 22:05:59 EDT 2017

On 2017-10-28 11:57 PM, Chris Angelico wrote:
> On Sun, Oct 29, 2017 at 12:46 PM, Soni L. <fakedme+py at gmail.com> wrote:
>> But you should be able to do things like
>> car = object()
>> car[Engine] = SimpleEngine()
>> car.[Engine].kickstart() # calls kickstart method with an instance of
>> SimpleEngine as `self`/first argument and `car` as second argument.
>> # etc
>> Which your decorator-based approach quite obviously doesn't let you.
> I think I follow what you're trying to do here. You want to have a way
> to refer to a subobject while letting it know about the parent. We
> already have something like that: when you call a function that was
> attached to a class, it gets to know which instance of that class you
> used to locate that function. Maybe there's a way to use descriptor
> protocol for this too?
> class SimpleEngine:
>      def kickstart(self, caller):
>          """*boot* Engine starts"""
> class Car:
>      Engine = magic(SimpleEngine)
> car = Car()
> When you look up car.Engine, it remembers a reference to car. Then you
> look up any callable from there, and it automatically provides an
> additional parameter. I'm not sure how the details would work, but in
> theory, this should be possible, right?

And how do you make the object creation so cheap to the point where it's 
actually practical? (quick question: does Python use a single opcode and 
an optimized codepath for method calls, or does it always create a 
method wrapper, even for immediate o.m() calls? If it's the latter then 
yeah I guess there's no reason for new syntax because it's not gonna be 
significantly slower than what we currently have...)

> ChrisA
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/

More information about the Python-ideas mailing list