def METHOD_NAME(self, proxyIndex):
    if not proxyIndex.isValid():
        return QModelIndex()
    row = self._map[proxyIndex.row()]
    if type(row) != int:
        return QModelIndex()
    #item = proxyIndex.internalPointer()
    item = self.sourceModel().item(row, proxyIndex.column())
    return self.sourceModel().indexFromItem(item)