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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 _get_mapper(self, mapper_name):
 """ Return the mapper based on the given name. :returns: the mapper based on the given ``mapper_name`` :raises: NotAcceptable if we don't support the requested format. """


        if mapper_name in self._datamappers:
            # mapper found
            return self._datamappers[mapper_name]
        else:
            # unsupported format
            return self._unknown_format(mapper_name)