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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 _prepare_ingest(self):
 """If the RDF datastream refers to the object by the default dummy uriref then we need to replace that dummy reference with a real one before we ingest the object."""


        # see also commentary on DigitalObject.DUMMY_URIREF
        self.replace_uri(self.obj.DUMMY_URIREF, self.obj.uriref)