def __get__(self, instance, owner):
        if instance is None:
            return self
        order = ListOption.__get__(self, instance, owner)
        components = []
        implementing_classes = []
        for impl in self.xtnpt.extensions(instance):
            implementing_classes.append(impl.__class__.__name__)
            if self.include_missing or impl.__class__.__name__ in order:
                components.append(impl)
        not_found = sorted(set(order) - set(implementing_classes))
        if not_found:
            raise ConfigurationError(
                tag_("Cannot find implementation(s) of the %(interface)s "
                     "interface named %(implementation)s. Please check "
                     "that the Component is enabled or update the option "
                     "%(option)s in trac.ini.",
                     interface=tag.code(self.xtnpt.interface.__name__),
                     implementation=tag(
                         (', ' if idx != 0 else None, tag.code(impl))
                         for idx, impl in enumerate(not_found)),
                     option=tag.code("[%s] %s" % (self.section, self.name))))

        def compare(x, y):
            x, y = x.__class__.__name__, y.__class__.__name__
            if x not in order:
                return int(y in order)
            if y not in order:
                return -int(x in order)
            return cmp(order.index(x), order.index(y))
        components.sort(compare)
        return components
dataset/ETHPy150Open edgewall/trac/trac/config.py/OrderedExtensionsOption.__get__/original