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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 slots(self):
 """Get all the slots for this node. :returns: The names of slots for this class. If the class doesn't define any slot, through the ``__slots__`` variable, then this function will return a None. Also, it will return None in the case the slots were not inferred. :rtype: list(str) or None """


        def grouped_slots():
            # Not interested in object, since it can't have slots.
            for cls in self.mro()[:-1]:
                try:
                    cls_slots = cls._slots()
                except NotImplementedError:
                    continue
                if cls_slots is not None:
                    yield from cls_slots
                else:
                    yield None

        if not self.newstyle:
            raise NotImplementedError(
                "The concept of slots is undefined for old-style classes."
            )

        slots = list(grouped_slots())
        if not all(slot is not None for slot in slots):
            return None

        return sorted(slots, key=lambda item: item.value)