[Python-ideas] abc.optionalabstractmethod

alex23 wuwei23 at gmail.com
Tue Aug 7 04:18:33 CEST 2012

On Aug 7, 10:35 am, Steven D'Aprano <st... at pearwood.info> wrote:
> But even putting that aside, the interface that it (implicitly?) documents is
> surely *required* interface. If you can neglect to override an abstract method
> with impunity, then it shouldn't have been an abstract method in the first place.

This I completely agree with. I don't understand the point of
declaring an abstract method that you cannot guarantee will be on an

Wouldn't it make more sense to define the optional aspect as a
secondary interface?

    import abc

    class IStarter(object):
        __metaclass__ = abc.ABCMeta

        def start(self):
            """start it up"""

    class IStopper(object):
        __metaclass__ = abc.ABCMeta

        def stop(self):
            """shut it down"""

    class StartOnly(object):
        def start(self):
            print "starting!"

    class StartAndStop(object):
        def start(self):
            print "starting!!"
        def stop(self):
            print "stopping!!"



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