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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 _init_hdrgo_sortby(self, hdrgo_sortby, sortby):
 """Initialize header sort function."""

        if hdrgo_sortby is not None:
            return hdrgo_sortby
        if sortby is not None:
            return sortby
        return self.sortby