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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 create_river(self, river, river_name=None):
 """ Create a river """

        if isinstance(river, River):
            body = river.serialize()
            river_name = river.name
        else:
            body = river
        return self._send_request('PUT', '/_river/%s/_meta' % river_name, body)