[Python-3000] Implementations: A syntax for extending method dispatching beyond type/class inheritance (original) (raw)

Dave Anderson python3000 at davious.org
Thu Dec 7 16:37:24 CET 2006

on 12/7/2006 10:06 AM Hasan Diwan wrote:

The parametrized version of the pass keyword could be used to indicate a formal interface.

I may be missing something here, but we already have a mechanism for defining that a object defines certain methods. Could we not keep it orthogonal and have, e. g.: class super(): def init(self): pass def typeOfSuper(self): pass(subclass) The way pass is defined now would remain the default. A new builtin pass() would be added to support your notion of interfaces.

I feel on a different page from you.

My best guess it is that

def typeOfSuper(self): pass(subclass)

is ceding its implementation to its subclasses, kind of like what an abstract class or interface would do

but I feel my guess is wrong. Please clarify.

def addkeyvaluepair(arg: MutableContainer.add, key, value): arg[key] = value def add(self, onemore): MutableContainer.add (self, onemore.key, onemore.value):

I'm not getting the insight you are trying to convey by contrasting these two functions.

The former is an example of someone writing a function whose first parameter is expected to be any object that is derived from MutableContainer (including dict), or is derived from a class that implements MutableContainer (including those implementing dict), or is derived from a class that specifically implements MutableContainer.add using a declaration like:

class CanAdd: implements MutableContainer.add

def add(self, key, value):
    ...

The later seems to be a class method which uses MutableContainer's add method to add any object that has a key and a value attribute.

More information about the Python-3000 mailing list