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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _set_backreferences(self, context, items, **kwargs):
 """Set the back references on the linked items This will set an annotation storage on the referenced items which point to the current context. """


        # Don't set any references during initialization.
        # This might cause a recursion error when calling `getRaw` to fetch the
        # current set UIDs!
        initializing = kwargs.get('_initializing_', False)
        if initializing:
            return

        # UID of the current object
        uid = api.get_uid(context)
        # current set UIDs
        raw = self.getRaw(context) or []
        # handle single reference fields
        if isinstance(raw, basestring):
            raw = [raw, ]
        cur = set(raw)
        # UIDs to be set
        new = set(map(api.get_uid, items))
        # removed UIDs
        removed = cur.difference(new)

        # Unlink removed UIDs from the source
        for uid in removed:
            source = api.get_object_by_uid(uid, None)
            if source is None:
                logger.warn("UID {} does not exist anymore".format(uid))
                continue
            self.unlink_reference(source, context)

        # Link backrefs
        for item in items:
            self.link_reference(item, context)