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Adding __implements__ to subclasses during ABCMeta.register (Python recipe) by Eric Snow
ActiveState Code (http://code.activestate.com/recipes/577712/)

This is an extension to the abc.ABCMeta class. It is related to recipe 577711.

Basically it has ABCMeta.register add __implements__ to any subclass that gets registered.

Python, 13 lines
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import abc

class ABCMeta(abc.ABCMeta):
    def register(cls, subclass):
        subclass = super(ABCMeta, cls).register(subclass)
        if not hasattr(subclass, "__implements__"):
            try:
                subclass.__implements__ = {cls}
            except TypeError:
                pass
        else:
            subclass.__implements__.add(cls)
        return subclass

This way a class can know what "interfaces" it implements.

Tags: abc