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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 _follow_leafref( self, xpath: "Expr", init: "TerminalNode") -> Optional["DataNode"]: """Return the data node referred to by a leafref path. Args: xpath: XPath expression compiled from a leafref path. init: initial context node """

        if isinstance(xpath, LocationPath):
            lft = self._follow_leafref(xpath.left, init)
            if lft is None:
                return None
            return lft._follow_leafref(xpath.right, init)
        elif isinstance(xpath, Step):
            if xpath.axis == Axis.parent:
                return self.data_parent()
            elif xpath.axis == Axis.child:
                if isinstance(self, InternalNode) and xpath.qname:
                    qname = (xpath.qname if xpath.qname[1]
                             else (xpath.qname[0], init.ns))
                    return self.get_data_child(*qname)
        elif isinstance(xpath, Root):
            return self.schema_root()
        return None