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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 _fetchAllChildren(self):
 """ Fetches the index if the showIndex member is True Descendants can override this function to add the subdevicions. """

        assert self.isSliceable, "No underlying pandas object: self._ndFrame is None"
        childItems = []
        if self._standAlone:
            childItems.append(self._createIndexRti(self._ndFrame.index, 'index'))
        return childItems