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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 index(self, row, column, parent):
 """ The index should point to the corresponding QtControl in the enaml object hierarchy. """

        item = parent.internalPointer()
        #: If the parent is None
        d = self.declaration if item is None else item.declaration
        if row < len(d._items):
            proxy = d._items[row].proxy
            assert isinstance(proxy, QtTreeViewItem), \
                "Invalid item {}".format(proxy)
        else:
            proxy = d.proxy
        return self.createIndex(row, column, proxy)